Rebooting / Restarting

my computer restarts without any pattern/reason that i could think off.

This has been going on generally for months.

This is a new computer that was bought in the end of September and it came with this problem when I bought it.

Was bought with windows xp, which was upgraded to vista and then to windows 7.

None of the operating system upgrades helped, but for a few months changing the graphics card did.

A few weeks back the restarts started again and just changing the graphic card this time didn't help. It went as bad as restarting once per minute. PER MINUTE.

The automatic restarts have been turned off.

This computer has been to the repairs more then my old one did in 5 years.

The next thing we will change is the motherboard.

Computer hasn't restarted in a hour so far, but each time I try to call someone on skype it ...lets me be on the call for a few minutes... and then restarts.

It restarts when I try to play world of warcraft, movies and what not. It sounds like the graphic card, but it's not. That's just today.

It started all over again a few weeks ago, then my dear repair guy reinstalled some drivers and it worked for a week. System restores don't work, but it doesn't make me stop trying.

I have ran every possible virus scan I can think of.

Reinstalled every program.

All kinds of system repairs.

I'm down to thinking it's either the power or system updates.

This is a rain of terror and It doesn't have a pattern.