If you want to restore your system back to the way it was shipped, when the system boots, immediately press the ctrl and F11 keys at the same time and you will enter the Dell Recovery Restore Utility.
You should have backed up any files that you may need after the restore completes because all the data on the system will be lost.
After you enter the Dell Recovery Restore Utility, just follow the instructions and the restore should complete in approximately 8-15 minutes, depending on how much data is to be restored.
When the restore is complete and the system reboots, you will need to enter all the user information as you did when you originally started the system.
When back to the desktop, you can then install any programs you may have used after you got your system and copy any files that you backed up.
Hope this helps.