Your hard drive has failed -- it's very possible the system is having trouble loading the video drivers from the portion of the drive that's unreadable.

Replace the drive and do a full reload - that should take care of everything.

Thank you,

currently i'm not in a position to reach dell service center.

so if i install the video drivers at some other location(like partition other than windows) will that work for few days?

Or if completely format the hard disk and again install the OS, will it help?

Run a chkdsk /f on the drive (open a command prompt with admin access and type chkdsk c: /f, and then restart the system).  That may get it working temporarily.

I wouldn't bother with a full restore of the system until the drive is replaced.

Thanks a lot...