What MT4 version, in what operating system?
Have you tried reinstall it?
What do you mean does not start?
With Windows 10 computer and 1045 MT4 version, you shouldn't have any problems.
What do you mean does not start? Doesn't open at all, or you can't login into your account?
I can't think of a possible problem, someone more experienced must come to the rescue...
Have you tried on a different computer?