1. Turn on the computer.
2. As the computer starts, press <F8> on the keyboard until the Advanced Boot Options menu appears on the screen.
3. Press the <Down Arrow> on the keyboard to select Repair Your Computer on the Advanced Boot Options menu, and then press <Enter>
4. Specify the language settings that you want, and then click <next>
5. Log in as a user who has administrative credentials, and then click OK
6. Select the last option, <Dell Data safe Restore and Emergency Backup>
7. Select the second option, <Select other system backup and more options> and click <next>
8. Select <Restore my computer> and click <next>
9. From the list click on <Factory Image> and click <next>
10. Click on <Restore without preserving new or changed files>
11. Click on Yes, to Continue
12. After the system formats and reinstalls the Factory image, click on Restart.
it worked for me,