Video card is crashing

[sdimejoker]

I am running a Sapphire Toxic HD 4870 512-MB on a Windows 7 64-bit OS. It is just over a year old and I have never had a problem with it before now. The game will open to the main menu and will let me click "start new game". Then, it will either open to the intro or make it to the first part when you have control of the character, at either point, the audio will continue but the screen will switch to white and green (usually) horizontal bars. I updated the driver on my video card and it didn't help. I really downloaded Amnesia and it didn't help. I changed the resolution off of the highest setting and all that did was cause it to give me multi-colored flashing squares when the game crashed. I know my video card can't be overheating because it barely gets started, plus I have 5 case fans on my desktop and on fan mounted directly on my video card. Any suggestions?