Can you explain a bit more what happened around the time the issues started? Did you update the system? Any hardware or software changes? As these can all help us better understand the condition your system is now in. Otherwise we will be giving you just very generic troubleshooting steps.
If the issue started happening recently I would recommend launching a System Restore. System Restore is a way to undo system changes by using restore points to return your system files and settings to an earlier point in time without affecting personal files of users. System Restore uses a feature called system protection that regularly creates and saves information about your PC's drivers, programs, registry, system files, and settings as restore points.
How To : Guide Perform a System Restore in Windows 10
The Start Menu and Cortana are features of Windows Specifically , so you may be looking at an issue with Windows itself. You can try repairing System Files with the DISM and SFC tool.
Type the following command into the Command Prompt window and press Enter to run a full system scan
" sfc /scannow " Without the Quotes
Note: You’ll need to do this from and Administrator Command Prompt window. To open one on Windows 10 or 8.1, right-click the Start button and select “Command Prompt (Admin)”. On all versions of Windows, you can also search the Start menu for Command Prompt, right-click it, and select Run as Administrator.
On Windows 10, 8.1, and 8, the Deployment Image & Servicing Management tool can fix component store corruption that prevents the SFC command from working properly. To run this command, open a Command Prompt as administrator. Type the following command and press Enter. DISM will check your Windows component store for corruption and automatically fix any problems it finds.
" DISM /Online /Cleanup-Image /RestoreHealth " Without Quotes
Allow the command to finish running before closing the Command Prompt window. This may take five to ten minutes. It’s normal for the progress bar to stay at 20 percent for a while, so don’t worry about that.
Please Post the Logs of the Repairs so we can see how they Span and What they Find. If it seems necessary , someone may create a repair from your logs that can help as well. Thanks.