Hi,
My name is Vishal and I work for the Social Media and Community Team at Dell. It seems that there is some Operating System Corruption. Hence you can try going in Safe Mode, using F8 at the start up once you see the Dell Logo Screen. If everything working fine in safe mode, then it could be hardware or software issue. If you are facing the same issue then it would be Operating System corruption.
You can also follow the steps in the following URL:
http://dell.to/JNHhlH
Hence just try the above steps and let us know if that helped you to isolate the issue.
Thanks,
Dell-Vishal S