Do a general cleanup of your computer.

To clean out unwanted files.

Start - Control Panel - Internet Options open -
Delete cookies, Delete files (select all off-line content) - Click OK to Exit.

Then go to Start - Run - Enter %temp% - Click OK - Click Edit - Click Select All - Delete.

Start - Run - Enter - C:\windows\temp - OK - and select everything except
temporary internet files, cookies and history folders and delete them.
If you don't see Temporary Internet files, cookies and History listed - select all and delete.
Then Restart your computer.

1. Error Checking- This takes about 35 minutes.
Start - my computer - right click local disk (C) - properties - Tools Tab -
Error checking section - Check now - check mark both boxes - Start -
This requires a restart to begin.

2. Start - Run - type - sfc /scannow - OK
Don't forget the space between c and /
You will need the Recovery CD that came with your PC if any thing is found wrong.
Don't insert unless asked for.

Then use the Defragmenter.
Start - All Programs - Accessories - System Tools - Defragmenter - Analyze and Defragment.

If you computer starts running better download CCleaner and use the Clean and Registry.

Un check the Recycle Bin and Run and anything else you don't want removed.
http://www.ccleaner.com/download/

avg antivirus is what I use. Free version.
http://free.grisoft.com/doc/2/lng/us/tpl/v5

When possible download and use Malewarebyte
http://www.malwarebytes.org/mbam.php

you say you got rid of Avast so what did you replace it with what antivirus are you now running to keep you protected?
Avast is a pretty lite AV what do you mean how it took over your pc?

what you are describing really sounds like an infection especially the part where you can not get your windows updates or access the site.

Try going here and running this free online scanner
FREE Online Virus Scan

did you update the malwarebytes and superantispyware before you ran their full scans on your pc? I would do that and run both again also.

"you say you got rid of Avast so what did you replace it with what antivirus are you now running to keep you protected?" .... Spybot, Superantispyware and MBAM.

"Avast is a pretty lite AV what do you mean how it took over your pc?" .... Everything started running very slow about the time I installed Avast. Uninstalled it and things ran back to normal ...for a while. Might not have been the Avast, but That's what I thought.

"what you are describing really sounds like an infection especially the part where you can not get your windows updates or access the site." .. Could be, but I can't find it.

"did you update the malwarebytes and superantispyware before you ran their full scans on your pc?" ... Yep. I would do that and run both again also.....Will do again.

Try this for the windows update issue

Go here and see if it works
Click Here
Fix any issues, then validate it.

If it still doesn't work try this:

Re-register the Windows Update DLL with the commands below:

* Click the Start button
* choose Run
* type cmd and then click OK.

Type the following commands. Press ENTER after each command.

regsvr32 wuapi.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll

Then attempt to run Windows Update again.

Make and model of computer?

Amount of Installed ram----> Opem My computer choose properties,Post that information

In my computer, place the mouse over Local Disk, a Window will pop up about hard drive size & free space, provide that information.

So, you have managed to uninstall your only virus protection (Avast) and now only have malware programs

"So, you have managed to uninstall your only virus protection (Avast) and now only have malware programs".....yep, guess I did. That'll be corrected soon as I get straightened out.

Zep......Dinosaur...Compaq Presario....hard drive - 35 GB, 19.3 GB free. 760 MB ram.

Woindows validated alright. Haven't tried update, yet.

You just can not run with out antivirus that is asking for trouble, but you also have a big issue with the fact your pc is old and has a lack of memory which in and of itself will cause it to run slow. the best thing you can do is add memory if the pc can take more, it is cheap and easy to do.
but number one is if you are going to be online put antivirus on it or don't get online. And what about a firewall? have one?

Did everything suggested. Tried to update...still get error message. Different one this time, though. Error code 0x800704DD. Not listed in their error code help page, either. Waiting to hear back from MS help desk. Meanwhile, I'll give Avast another go. But, this dino is running a bit back to normal.

Aufin,
Check the link see if anything here is helpful

Here is a link that might be useful: h2g