Mmmm. Lets try something:
1. Download and try to install the FREE version of Malwarebytes
2. Run a FULL scan if possible
3. If it finds threats, make a note of them for posting back here, and delete them if you get the option.
4. After scanning and removal is complete, reboot your system and log in as normal
5. Scan with Malwarebytes again.
6. If nothing is found, try and update Windows - if it can't update, post the error code here.