Firefox not opening

I use Windows XP professional. Of late I am not able to open Mozilla Firefox in my PC. But when I try to close the computer, I get a message "Firefox exe running ". I uninstalled and reinstalled the program, with the same result. Can someone please help me out of this situation?

 

Since you said "of late" you haven't been able to open Firefox, does that mean that it did work at one time?

 

Whatever the situation, it is never fixed by uninstalling and reinstallating, but, rather if there is no other recourse, by creating a new profile.
But, info is needed, with some past history, if any.

 

of course, it has been running perfectly well before

 

Fine, but what version was running perfectly? The same one used now?
Occasionally, I have problem similar to yours, but all I do is to open the Task Manager (Cntrl+Alt+Del), locate firefox.exe, delete it. After doing that it starts fine.
But, I have a good excuse. I have four Firefox versions, run with four different profiles, and, if I close one, and try to open another one, too soon, the original is still open in the Task Manager. Usually, I count till ten, before trying to open another version.