I think the some OS Important system files damaged during reboot, sfc / scannow , but still You must conduct a thorough investigation to find out the reasons for the restart, trace the system tools / administrative event previews
Make sure your drivers are up to date and not corrupt ( I know you've been installing software recently, make sure that's not the culprit as well) If they are and it still happens set a custom paging file size. Last it could be your RAM.