Hello alig7, welcome to Seven Forums!
Here are the instructions to recover the PC to factory conditions, be advised
that this will over-write all the data on the PC and it will not be recoverable if this process is successful; be sure to post back with any further questions you may have and to keep us informed.
Here are the recovery instructions from Dell.
1. Reboot, and press Ctrl + F11 at the Dell logo.
2. The Dell™ PC Restore by Symantec screen will come up.
3. Select "Restore" or use the Tab key to highlight it and press Enter.
4. if you wish to continue, click "Confirm", or use the Tab key to highlight it and press Enter.
5. When the utility is finished, click "Finish", or use the Tab key to highlight it and press Enter.