System Restore to a restore point BEFORE the problem began?

If not your best bet is to FIRST do malware scans while in Safe Mode with:
RKILL - run it FIRST and then run the next two scans BEFORE any re-booting)
MalwareBytes
Super Anti-Spyware

If they don't get your system cleaned up you need to ensure you have ALL your data files backed up (on external drive, flash drive, CD or DVD etc) then restore the computer to factory specks with their recovery disks or their recovery image on the hard drive.

Can't tell you which for your computer as you didn't see fit to tell us anything such as, Model, Operating System, etc but the Dells normally have a recovery partition you access by pressing the CTRL + F11 (at the same time) at the Dell Screen when the computer first turns on. Be sure to press and release the keys at the same time to access it. That may not work with your Operating system as the process varies by OS and even model.