Computer shutting down out of nowhere

[dragflameson]

Is there a specific way to find out what is going wrong exactly, without having to use trial and error? Is there maybe and error log or something I can look at after it happens?

I think I might need a new power supply, but I'm not sure...

I'm running Windows XP. Basically the computer will just shut down unexpectedly while in use. I leave the computer running 24/7 and it never happens while it's idle. It always happens while I am doing something.

For example, it always happens while I am scanning with Malwarebytes, or randomly when I'm browsing with IE 7, or when I am using TurboTax.

Now when I say "shut down" what I mean exactly is the monitor will just all the sudden turn completely black and display the "no connection / check connection" message as if the computer was off and then a second later I see the BIOS post screen and the computer begins to boot normally as if it had been off and then was powered on by pressing the power button. There is no Windows logoff screen or "saving settings" screen like you would normally see when the computer shuts down correctly. Its just there one second and then a black screen the next second. Funny thing is... when it boots back into Windows I dont get that screen that says, "computer was shut down incorrectly" where it gives you the different options to choose from where one of the options is to "use the last known good configuration". It just goes straight back into Windows as it normally would if the computer had been shut down correctly.

Its almost like what would happen if you were to reach over and hit the restart button on your PC while you were in the middle of using it. It turns off and back on so fast that the computer never actually sounds like it was ever off. I do hear the hard drives shut down and start to spin up again though when it happens. It happens so fast.

There are no viruses or spyware... so please dont ask me to scan and make sure my computer is clean. It's running perfectly fine expect for when it decides to shut off.

I know this is a hardware issue and I think its the power supply. The reason I think this is because the power supply is at least 2.5yrs old now, I leave my computer on 24/7, there are 4 internal hard drives, one internal DVDROM, my mouse charges off the PC, it doesnt happen while idle, only when its doing something, ect. It just seems like this power supply has really been getting worked over the past 2 years!

Anyways, what do you guys think?

I'd like to get a better idea before I go out and buy a new power supply.

Thank you!