Question : Problem: Computer powers off without warning

I have a Sony Vaio VGC-RB53 desktop, P4 3Ghz, 512 MB with a CD/DVD burner, multi-card reader and Windows XP Home. It is just over a year old but I have been having the same problem to varying degrees for 3 months.
SYMPTOMS:
My computer powers off without warning. Sometimes it will restart after I unplug and plug the power cord back in, yet other times it will take days before it will turn on. When it does restart, it has been known to shut down immediately, yet other times it acts as if nothing is wrong for days. The fan is loud when it first restarts but then subsides until the next power out. When it shuts down abruptly, I’ve noticed that the light in the back of the computer (power supply I think) and the small light on the motherboard goes out. There have been times that I’ve turned the computer off normally at night (with these lights still on) but the next morning, both were off and I had to replug the cord again to turn the computer on. Now the computer won’t restart. The lights are out, I replug, the lights come on, I hit the power button and the lights go out.
EVENTS:
I have tried to narrow down the times this stuff would happen, but there seems to be no specific pattern. It has happened while booting up, within Windows, and when shutting down.. It has done it in ‘safe mode’, while downloading, while in different software, and one time it powered off when I was putting a CD in the tray. I had to replug again, and it stayed on long enough for the tray to go back in and shut off again. It has also powered off while doing nothing.
ACTIONS:
1. Thought it could be overheating, so I installed ‘SpeedFan’. Temp runs mostly in the lower 40's, but has reached 60 once when editing video.  What puzzles me is that when it reached 60, it never powered off but another time, it shut down at 42.
2. I checked for viruses, adware, spyware and didn’t find anything.
3. Cleaned out the computer. It ran alright for 4 days, so I thought it was fixed until it acted up again.
4. Checked surge protector. It was alright but I plugged the computer into a wall socket until it powered off again.
5. Removed all cables except mouse, display and keyboard.
6. Used ‘system restore’ to prior time, Checked ‘Power Management’, Tried ‘safe mode’

Answer : Problem: Computer powers off without warning

Get another, if possible stronger Powersupply.

If that doesn't help it is most likely a bad motherboard. Check it for bad Caps (bulging, leaking or cracking signs on the capacitors).

Also run your system for a longer period of time using an alternative OS that starts directly off CD, like knoppix.

http://knoppix.net