Might be unuseful, but I really used many hours figuring this out, since information on the problem is rather limited...
Anyway, I had MySQL installed, but uninstalled it, and when I wanted it back I got stuck on configuration. -Got stuck on "Starting Services" or "Applying security settings". Really pissed me off at times
Fixing this, however, isn't tough at all, once you know what to do.
On vista you do the "start search" from start menu (in the bottom). Type "regedit" and press enter. Go to HKEY_LOCAL_MACHINE-->SYSTEM-->CurrentControlSet-->Services
There you find MySQL and delete it.
After this you go to controlpanel and uninstall MySQL as you normally would.
Go your MySQL directory and delete what ever might be leftover.
Finally in cmd you time "sc delete mysql"
We may be doing some double work here, but this is what I did, and it helped.
On XP, you do the same as above, except that you open regedit through the "run"-function (it might be regedit32, if regedit dont work)
Hope this helps someone one day, and if not, I just wasted 15 minutes writing this
Now I think i've posted it in the right category... Sorry if not...