I would also download, install and update
Malwarebytes full scan in Safe Mode with Networking. If you can't get boot into that, download on another computer
Microsoft Standalone System Sweeper write to flash stick or CD, boot to run a Full Scan.
Once the system is cleaned up, you'll likely need to repair System files as described, if necessary from
System Recovery Options Command Line:
SFC -SCANNOW Run in Command Prompt at Boot
I would also try
Startup Repair several times and System Restore from the Recovery Options on F8 Repair My Computer menu, or DVD/Repair CD.