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.