Windows 7 - Sudden Shut down only at Windows Seven

Hello people
I have installed windows Seven along with Ubuntu 9.10 awhile ago.
I had encountred several sudden shut downs during the format process while installing XP that's why i went for Seven. Whenever I'm using Windows 7 the computer shuts down by itself at random times. It's like i pull the power supply cables. When I want to restart it, it fails. It only works after few attempts.
I have confronted the same problem with Windows XP before, but that was only when I run Photoshop/Illustrator CS3 along with other softwares (like Messenger, media player/vlc, or anything else). But it wasn't with the same rate as with Seven. But with Ubuntu, i can spend like 12 hours without any sudden shut down at all ! (i only had it once while trying to install Windows 98 on VirtualBox !).
I have three partitions, one for Windows 7, one for Ubuntu, and one shared.
I tried to go back to XP but it kept shutting down while formatting.
Some people told me that it is because of Ubuntu 9.10 but I fail to comprehend why because Windows (XP or Seven) cannot recognize the Linux partition (EXT3 or sth).
I have a pantium 4 3.2Ghz, 1GB RAM (512 X 2), ATI Radeon X1300, 160 HD ( along with the same one, but external).
Any help is appreaciated !
Thank you guys

Could it be your power supply or something?

If it was the power supply, then why does it work perfectly on Ubuntu ?
If there is any way to make Windows Seven consume the least hardware, let me know please.

You've got a real mystery on your hands, there.

The best I can suggest is that when it does it, write down --keep a handwritten log-- of when it happens and see if any pattern emerges... For example: Does it do it while accessing a specific drive, does it do it only when flash drives are inserted, etc.

Also check your BIOS... if you're overclocking, revert to stock settings. Check your hardware monitor, is it running hot? etc.

Well, yesterday while starting this thread, it didn't shut down by itself as usual, i was on it for like an hour and then i turned it off by myself.
I even run Photohop + Illustrator + firefox at the same time, it was running slow but it didn't shut down. I haven't notice any specific pattern, it does it even when i'm just surfing the net. can you tell me how to revert to stock settings (do you mean get back default setting?) and to know whether my hardware are running hot or not. Thanks peeps.