Sounds like you might have to backup your data and then try clean installing Windows 7:
If that doesn't work, you might have a hardware problem.
Boo.. i was hoping to avoid this... I may just buy a new comp since I have to reinstall all my software anyway, might as well buy a computer from a different vendor... Three dell comps in three years isn't a good sign (XPS died, replaced by this Alienware Aurora, now this one is having issues... Inspiron Mini 10 died after 10 months).
If you want to spend $1000 or more on a new PC ... go for it.
You can reinstall Windows and core drivers in 30-60 minutes. The reason I suggested a complete re-install is because it sounds like your Windows install is corrupt. How did it get that way? ... Virus infection? I'm not sure, but that's why I mentioned a possible hardware problem (HDD failure maybe)?