How long is the computer on before it turns off..If you have a desktop computer, how long has it been since the inside of the tower was cleaned, dustbunnies etc..
If a laptop, same sort of question

Gale-
I think the suggestion from genes is the best first approach. Computers that get dirty/dusty inside have heat issues and tend to shutdown because of this.

On the other hand, a System Restore won't hurt anything. And remember, for basic questions like this, Google is your friend...

Here is a link that might be useful: XP Restore

it could be a power supply getting ready to give out and it could well be heat related as mentioned if this tower has not been opened and cleaned out recently. you can find a lot of guides for that one google and some videos like this one
Cleaning the Inside of Your Computer Tips

Tks, everyone. Computer stays on all day. With my arm in a sling it's about all I can do right now.

I'll have it cleaned out tomorrow and see if that helps. Will let you know how it goes.

Another thing, I've been watching a lot of NetFlix and Hulu and it's become impossible to do because I have to reload so often. Truly aggravating.

Tks again.

You might also want to make sure that the tower is well ventilated and not enclosed in a cupboard or anything blocking the vents/Fans

Gale: dont want to overdo the protection, but make sure its turned off and unplugged before you open it up..be mindful that it is electronics are therefore pretty delicate

FYI, we did the cleaning of the computer and it wasn't very dusty at all. Surprised me because it's been too long since we did it.

Still having the problem of it cutting off, sometimes it will come back to the same place and sometimes I have to reboot. Also can't watch NetFlix or Hulu. I don't have any problems with YouTube.

So far I've done the following:

Defragged
Disc CleanUp

Ran these programs that we've been running for a long time, the paid versions.

Malwarebytes
AVG Antivirus
Super AntiSpyware

While they've all gotten rid of a lot of 'unneeded stuff', they haven't solved the problem.

I'm at my wit's end here. Any other ideas?

Signed,
Frustrated in Texas

Perhaps you might see something that gives you a hint in ... Event Viewer. System logs.
Right click MyComputer / Manage. Usually.

Might open Task Manager - maybe a hint there too, with processes - check the lower box for show all.
click 2x the Cpu heading .. see what process %'s are
Maybe also the Memory heading ... see the higher users.

Perhaps the power cord..try wiggling it around and see if it knocks off and on..If not and you still feel you would like to try and system restore back a few days etc..then Programs>Accessories>System Tools>System restore then pick a date before this started..

Also now that you have determined that the heatsink over the processor is not clogged with dust try leaving the side panel off temporarily and see if that helps. If the computer still quits use a small house fan blowing in for a while. These 2 things will either indicate heat or eliminate heat as the problem for sure. Maybe a fan is not working as it should.

It might be the power supply failing . That is what happened to my husband's desktop. My youngest son has it up in Va. right now trying to find another motherboard to go in it since the power supply damaged the motherboard when it failed.