Umm, are you saying you do not have the original Windows XP CD? You are right, at 5 years old there seems little point in spending big bucks fixing this when a new machine might cost a few $$$ more than the price of fixing. However.......

Tell us what anti virus, anti spyware and firewall programs you are using. Also note for us when you last updated any of them and ran tests. (Update and run them now so we know you have tried some programs at least)

If you are able to use it under limited user status it has hardly crashed big time. When the store had the computer did they remove the side panels and check for dust bunnies? Unplug the power cord, remove the left side and look inside for dust covering the Heatsink - the big block under the fan on the motherboard. Leave the left side off for a while and see if it continues to run with the better air circulation (this is a temporary fix)

Thank you for your quick response. We bought this computer of somebody who fixes and sells secondhand computers, I think maybe something is dodgy if we are missing original Windows XP CD so i hope I did not get myself into trouble? How it was explained to us I understood it to be crashed, but what you say makes sense and I will check for dust bunnies too!
We have been using AVG8 Free antivirus and I'm not at home right now so can't see when it was updated last. I don't think we can update it in the limited user account but I will see tonight. The firewall program I'm not sure of either. Thank you for giving me some ideas, much appreciated!

Might want to try to start in Safe Mode by tapping the F8 key on boot.
Once in Safe Mode, navigate to System Restore.
Start button/All Programs/Accessories/System Tools/System Restore, and see if you can restore to an earlier time before this problem occurred.

I find it somewhat odd the computer only fails (Reboots) on login to the admin account and runs fine on the Limited account, how limited is the limited account? can you download from that account?

It's (possible) you may be able to access the admin account in Safe Mode I would try it just to see if you can access it, then follow randy ca advice on system restore, these are just other things you can try if it turns out not to be heat related.

Here are directions for Entering the Safe mode:

Using the F8 Method

1. Restart your computer.
   
   2. When the machine first starts again it will generally list some equipment that is installed in your machine, amount of memory, hard drives installed etc. At this point you should gently tap the F8 key repeatedly until you are presented with a Windows XP Advanced Options menu.
   
   3. Select the option for Safe Mode using the arrow keys.
   
   4. Then press enter on your keyboard to boot into Safe Mode.
   
   5. Do whatever tasks you require and when you are done reboot to boot back into normal mode.

The other item to consider is the computer maybe Blue Screening as soon as you try to log in to the Admin account. We can address that if needed.. When a Blue Screen error occurs Windows restarts so fast you do not get time to actually see the error, there is a way to stop that so you can read the error if we should need to, System restore may resolve it.

On another note I would have to think the computer shop has been all through this.

What is the Make and Model?

Just a quick update:

You guys are the best! I'm stoked that I got all this helpful advice and yes I did start the computer up in SAFE mode. 'Crashed big time?' What was I on about??

Not quite there yet, but a good start;
I started the computer up in the safe mode and this worked. However I can't restore the system to an earlier time. I go through the steps and when I click to confirm this action nothing happens. When I clicked on help this message came up: windows cannot open help & support because a system service is not running. To fix this problem, start the service named help & support.

I was able to use the computer in safe mode, to look into my files etc.

Another message came up as well:
ConnAPI.DLL Re-installing the application may fix this problem

Does this make sense? Thank you so much for your help!

do you have any Nokia apps on your pc? you might check this info from bleepingcomputer forums.

connapi.dll is a Connectivity API from Nokia belonging to PC Connectivity Solution
found also :
"A web search shows the connapi.dll is related to cell phone
communication software. My suspicion is that you have a twain scanner or
camera driver installed that relies on this DLL file. Reinstalling the device driver should correct this error."
from this forum post
Connapi.DLL

Here is a link that might be useful: bleepingcomputer

I remember having a problem with Help & Support a while back. If you go to Start-Run, type in misconfg and click on Services. You can restart Help & Support from there (I believe). It should show in the list and you can check the box to restart it.

It was a while ago, but I remember it caused a problem on my machine.

Jane

See if you can run this program since there are 3 accounts lets make sure there is no malware present,

Please download Malwarebytes' Anti-Malware to your desktop. Click here
* Double-click mbam-setup.exe and follow the prompts to install the program.
* At the end, be sure a checkmark is placed next to Update Malwarebytes' Anti-Malware and Launch Malwarebytes' Anti-Malware, then click Finish.
* If an update is found, it will download and install the latest version.
* Once the program has loaded, select Perform full scan, then click Scan.
* When the scan is complete, click OK, then Show Results to view the results.
* Be sure that everything is checked, and click Remove Selected.
 The log is automatically saved by MBAM and can be viewed by clicking the Logs tab in MBAM.
The log can also be found here: C:\Documents and Settings\Username\Application Data\Malwarebytes\Malwarebytes' Anti-Malware\Logs\log-date.txt

 Copy and Paste the entire report in your next reply.

Extra Note: If MBAM encounters a file that is difficult to remove, you will be presented with 1 of 2 prompts, click OK to either and let MBAM proceed with the disinfection process, if asked to restart the computer, please do so immediately.

"I think maybe something is dodgy if we are missing original Windows XP CD"

You've got plenty of good help with your problem but just wanted to let you know it's common not to have the original Windows XP CD. I bought mine new with XP installed and at that time CD's weren't included. SIL bought almost the same thing six months later and they were included again.

Add to that the people who lose them or don't bother to bring them in with their trade-in and you've got no CD.

Thanks again for the further advice. I have tried to look at the Bluescreening but I can't do a system restore so I don't know how to look at it. It will not let me do a system restore to an earlier date (in the admin account)

I will try to download the Anti-Malware but the internet connection is completely insecure now because the AVG8 Update is not working anymore, it keeps giving the message that the update has failed. I'm worried about going onto the internet now, what if I make it even worse?
In the limited accounts I can't download anything because they have limited access, and the internet connection in those is just as insecure anyway.
I'm not sure when AVG updated last, maybe I can find that in the System Restore calender, I'll have a look.

We used Integard as a protector for the kids to not go into bad websites and we now get messages as well that this program is damaged.

As for the make and model of this machine, we have no idea. There is no brand name on it and the shop couldn't find anything either.
It's a real mess I'm afraid..

We are going on holidays tomorrow but I will try the last couple of tips tonight and after I will probably go and throw the thing out the window, or I let you guys know next week if I change my mind and struggle on, hahaha

You could download malwarebytes to a flash drive or memory stick from a good computer the insert it on the bad one and try that,

(You are right you have a lot of issues here) it looks as though you may have windows files missing I'm guessing here, but that may be the reason the shop wanted an xp cd to try and reinstall or do a repair,as owbist first said I would not put any money in it + it is 5 years old, maybe time for computer under the tree....Just my opinion.