Sometimes your original account is corrupted in some obscure way, and switching to a new account is the only way to be able to use that program again, even if you don't like that idea.
Sometimes it's some setting you changed or some malware running in your account and then you'll have to find out what it is to fix it.
The easiest way in both cases might be a System Restore back to when it worked, or - if you have that - restoring an image backup of your c:-drive you made when it still worked.
There are times when programs (in this case, Free Download Manager) does not work any more but if I create a new user account it works again. How do I get the program to function correctly again in my original account on the same computer? I do not want to migrate to a new user account.