I know you said you ran SFC but I'd run it again from an elevated command prompt (option two.) Even if problems aren't found, run the scan 3 times and reboot the computer after each scan.
SFC /SCANNOW Command - System File Checker
You could also check for malware by running full scans with your installed anti-virus suite and then run a couple of on-demand scans with Malwarebytes
and ESET Online Scanner