Sudden Instant PC shutdown + no restart

Greeting Majorgeeks, hopefully someone here can help me with this problem.

For a while now, my computer has had sudden crashes, with no warning, where it shuts down and won't restart; I got to unplug it from power for 5-10 seconds and plug it back in, at which point it will start booting up right away.

Now, my first idea would have been the RAM, but the problem does get stranger.
EDIT: Actually my initial idea was that my computer was overheating, until I found out about running low/mid end games making it stable, seems that should not prevent my comp from overheating

If I run a program that requires graphix, i.e. a game, even in the background, my computer is 100% stable.
BUT if I run a high end game, like skyrim, it will also crash suddenly in excatly the same way as mentioned above


For a long time, this has puzzled me, but then I thought I had the answer; I know the GFX card uses both some of it's own ram, but can also use the computers normal ram to boost it's performance.

So I figured that a game makes the computer reserve one of my 3 ram sockets of 2gb, but won't actually use it with low end games because it doesn't need to extra boost.

If the ram socket reserved for this the faulty ram, then running no game would mean the computer would eventually use it for various tasks and crash
Low end games would reserve it, but not use it = no crash
High end games would reserve it, and then use it = crash

But now I tried plugging out the sticks of ram 1 at a time, and running the system with the 2 remaining sticks, but no matter which stick I remove (and which DIMM sockets I plug the remaining 2 sticks into), the system still crashes unless I run a low/mid end game.

Would this sound like a powersupply issue perhaps?

 

Whoa up!

Take your time, describe what happens and what's running when it crashes.

State your hardware (PC/laptop specs, make and model #, details inc.make/model of all components if custom, and running software) OS +SP level, A/V, firewall + any other running programs when it happens.

I'm guessing 6GB RAM w/W7x64 and an add-in gfx card but I'd like to know for sure.

If you can't be bothered to go through those steps - quick and dirty answer = could be PSU, could be bad caps, could be something else entirely.

 

Try it in safe mode.

If the PC doesn't crash in Safe Mode, it's likely a driver issue or something that's corrupted in the Windows registry.

If it does the same thing in Safe Mode my first suspect would be the video card, followed by the power supply.

 

PC Desktop, Packard Bell, "imedia A3851 NC", everything inside as when purchased, no customization.
Windows 7 home premium 64-bit
AMD Athlon II X2 215 dual core processor
ATI Radeon HD 5570 1024MB
640gb HD
6gb DDR3

I will try that later today and edit in the result of running in safe mode here, once I have.