"If your operating system is VISTA / Win 7, tap F8 key when you see the dell logo. It will take you to advanced boot menu options under which you will see Repair your Computer, Select that option and enter your password if it asked, then you will be seeing list of options like system restore, command prompt, etc., In that the last option says Dell PC restore or something like that. Select that option and follow the screens.. That's it.
* Start the computer.
* As the computer starts, press the F8 key until the Advanced Boot Options menu appears on the screen.
* Press the (Down Arrow) to select Repair Your Computer on the Advanced Boot Options menu, and then press Enter.
* Specify the language settings that you want, and then click Next.
* Log in as a user who has administrative credentials, and then click OK.
* Click Dell Factory Image Restore.
* In the Dell Factory Image Restore window, click Next.
* Click to select the check box for Yes, reformat hard drive and restore system software to factory condition.
* Click Next. The computer is restored to the default factory configuration.
* When the restore operation is completed, click Finish to restart the computer."
If this does not work for you it means that your recovery partition has vanished.
Corrupt or deleted. You then are faced with a manual install.