Random Standby Mode!

Hi there - new to these forums.

I have posted this in the Graphics Cards section since I think that is the issue and I could not see a more appropriate section.

First off my specs:
Asus EN7950GT Gfx Card
Asus P5W DH Deluxe Motherboard
2gb ddr2 667Mhz Ram
Intel Core2 Duo 6600 @ 2.4Ghz
Windows XP Service Pack 3
450w Power Supply

For a few weeks now my screen will randomly go into stanby mode (is the green light goes orange and it displays "going into standby mode" ) 99% of the time this occurs when I am playing games, nothing fancy just World of Warcraft, Frets on Fire and especially TrackMania. A few times though it has happened when just browsing the web or folders etc. But hardly ever. If i rapidly shake the mouse or mash some keys it sometimes comes out of stanby and I can continue playing or what ever I was doing, however most of the time I have to restart my system. Prior to this I have had weird issues where my screen would be filled with multi color blocks like an 80's arcade game gone wrong or the display would be fuzzy or low resolution on bootup, however that is passed just this standby mode issue. I have always assumed its the graphics card or power supply, since then I have replaced the power supply and it still happens. I need to just check what you guys think before I go out and buy a new graphics card since they arent the cheapest of things

Just to clarify, it happens randomly, I have formatted and reinstalled windows xp and the newest drivers many many times, I have tried with a different monitor with the same problem still occuring, I have taken off the side cover and put a desktop fan blowing straight into the pc - thinking it was a heat issue - same problem. So in my opinion it is the graphics card, as I said I just need some clarification or some more things to rule out other causes.

Thanks so much,
Ross

Also check any power options in the bios.

Check your GPU and CPU temperatures, when this happens.
Take the side off and blow a fan at the graphics card while gaming.

Run Prime95 and memtest86+. Check for errors.
Check your CPU temperature while running Prime95.

Ok memtest86 returned 0 errors. prime95 returned 0 errors. I am stumped. Tomorow I will be taking my pc to my uncles house where I can inter-change parts to determine what is wrong. The screen went black during the memtest86 scan which just shows me that its not a silly setting in Windows. Hate it when things don't completely break. I would rather the broken component fry and have smoke gushing out of it so I can tell whats broken ty anyway evongugg I will post back with the solution for future reference ^^