Hi guys, I uninstalled a theme and went back to the Windows 10 background picture that originally came with the Windows 10 and ever since then, the start menu comes on and disappears, if I booth the system the start menu will come on and immediately the system is fully on, the start menu disappears again, I had to go to the task manager and click on Windows explorer to restart and the start menu appears again and disappears after some seconds but if I keep clicking repeatedly once it appears, it tend to stay but if i shut down the system, I have to start all over again to bring it out following the method I mentioned above.

what should I do and how can I get it back there the way it was before, someone told me to install a new Windows that it has been corrupted by the theme I used and uninstalled but i cannot afford to lose my documents, files and softwares and start afresh.
please is there any way out to bring back the start menu to original position without me going through the task manager in which it still disappears after some seconds