Driver trouble (Radeon HD 6670)

Hello,
I bought a low end gaming cyberpower pre-assembled pc about a year ago that is running windows 7 64 bit. It came all set up and for the most part I have not had any problems with it. But ever since I got it, I have occasionally had trouble with the gpu (Radeon hd 6670). Sometimes when I boot it up, the computer is good, but the card doesn't seem to work. I get nothing on the monitor even though the computer is fired up. I have been using the stock gpu in the motherboard when this happens. It works okay, but absolutely no power. I tried to find a driver that they sent with the computer, but I couldn't find anything that they might have sent. I have tried downloading the drivers and catalyst support software from AMD, but it does nothing.

The only clue I know is that when it doesn't work, it usually puts up a error message of some kind that says the ati support driver is no longer working or something like that. But I don't know more then that.

So I don't know what to do. Any help would be much appreciated!

Thanks,
Nathan