Welcome, you may want to try this. It should bring you back to factory specs. The day it was when you brought it home.
Here are the recovery instructions from Dell
1. Reboot, and press Ctrl + F11 at the Dell
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.
The bad news is many times when you put another installation, as you did, the restore capablity is not longer possible, even though the partition is still present.
I do wish you luck