Vertical dashes and dots on dell logo scr...

Hi, I have bought a second hand Dell Inspiron XPS M170 from ebay. It seems to function well in every aspect other than I think I have a graphics card problem. The card is an Nvidia GeForce 7800 GTX 256mb. Here's what happens, when you boot up, the black screen with the Dell logo is covered in lots of little blue vertical dashes and dots , which are formed into vertical stripes. The next screen is black covered in lots of 'O's with dots in the middles of them which look like lots of cartoon eyes lol! Then the windows XP splash screen does it's thing and instead of going to the login page, the screen goes blank but there is still a very faint glow at the bottom for about 10 seconds. Then suddenly, the screen switches off! The actual processor is still on though. It's like it is going into hibernation, but with no chance of ever going on again. The only thing to do is to manually restart it with the power button. The only options open to me at this point is to start it in safe mode of restore it tp a previous point when all the settings worked.

I've tried downloading updated drivers from the nvidia site but that didn't work. Can anyone help??

I got this laptop for £360 and don't want to pay another £230 for a used card! Is there anything I can do?

Please help!!