Graphics card preventing windows login??

Hello,

I'm not computer saavy but I have a problem with my dell studio XPS 435MT not always showing the Windows login screen in normal mode, all I get is a black screen with a mouse cursor after the emblem appears. This started happening after I updated drivers on my radeon HD 4250, so I tried system restore and redownloaded the driver but still same problem. So I system restored again without updating the driver and still the same problem. I upgraded from Vista to 7 hoping this would solve the issue but it didn't. My computer runs fine after I enter my login (when it does show) but I've noticed a slight lag in performance. BTW windows always starts up properly in safe mode.

Is it my graphics card? I think it is because I've run every diagnostics I could find and nothing shows abnormal. I wonder if my graphics card is becoming obsolete or nearing it's life cycle. I'm contemplating upgrading to AMD Radeon 7750 with a compatible 500W power supply. I'm on a tight budget so any help will be greatly appreciated for a newbie like me!