Run Startup Repair, as follows:
Click Start
Click Settings
Click Update & Security
Click Recovery
Under Advanced Startup, click Restart Now
Click Troubleshoot
Click Advanced Options
Click Startup Repair
Select your account (if necessary)
Type your account password (if necessary)
Click Continue
If there's a problem with your Startup files, it should be fixed. If you see "Start Repair couldn't repair your PC", it means that no problem was detected.
Then, irrespective of whether a problem was detected by the above, run a disk check as well:
Click Start
Type cmd in the search box.
In the results field above, RIGHT-click on cmd and select Run As Administrator
Then, assuming that your hard drive is Drive D on your computer, type CHKDSK d: /f (NB: There's a space in there after the K and another one after the colon)
Hit Enter