|I hope you already made backups of your own files, as without backups you will lose them if, such as now, you need to re-install Windows or perform a factory-default recovery.|
With luck there will be a hidden partition on the hard drive. It contains a backup of everything that was pre-installed when the computer was purchased new.
This only applies to certain models though.
Start the computer with all peripherals disconnected except kb, mouse, & monitor. As soon as you see the 'Dell' splash-screen, press and hold the Ctrl key then press F11
This should start the recovery program if your computer has that feature.
Now release both keys.
More info on that procedure here: