You can check the file system for errors like this:
- boot your computer into 
Safe Mode (see the video tutorial below)
- search for 
Command Prompt (just type Command in the menu search box)
- right-click on it and select 
run as administrator
- type 
sfc /scannow inside the command prompt and press Enter
Booting into Safe Mode:
	
	
You should also check for malware, install 
Malwarebytes while in Safe Mode and scan your computer.