1) Please to to Windows Update and see whether you can get the latest
definition updates for Windows Defender.
Choose Custom, rather than Express.
2) Then try restarting in safe mode by pressing the F8 function key before
the first Windows screen appears. I usually tap it about once a second
after the screen turns black on the restart.
Choose safe mode. Once Windows comes up, see if you can run Windows
Defender in this condition, and do a quickscan. If the quickscan finds and
removes anything, follow that up with a full scan.
It is a good idea to have updated your antivirus, and to also do scans with
the antivirus in safe mode, if possible.