^^ That's a good suggestion by theog which you should do first and check to see any repair action will make your laptop bootable. (If you succeed in booting, the first thing you should do is to backup the OEM activation with Advanced Tokens Manager. http://www.sevenforums.com/windows-u...s-manager.html
How old is your DELL laptop? Is it still under warranty?
If it is, then my advice will be to contact DELL technical support and check if they could help you. Dell support has always been good.
Did you make the Recovery Disks when you first received the laptop?
Do not rush to clean install on your own right now.
Even if your laptop is not under warranty, you may request for a OEM Reinstall Disk ( you are entitled to it) and Dell will send it free. ( A clean install with it will retain OEM activation and you will not be required to activate by any means.)
In the meantime you can try all suggestions by the experts here.(except a clean install)