1. Run a scan with your Antivirus
2. Run a scan with Malwarebytes
3. Run with, say, CCleaner. Get rid of junk, defrag your HDD, check the registry.
4. If you have installed new programs, check them = preferably get rid of them. You may have something unwanted installed, attachments are more and more common - you get what you never intended to get.
Of course it's possible your computer is going down, but that's commonly quite unlikely.
All for now, best wishes.