I could not launch MC to a state I could interact with it at all except to kill it via task manager.
I have, on occasion, had this happen... What I have found is that it typically occurs after MC stops responding (for whatever reason) and I have to "force close" the application. After this, you can no longer get MC's GUI to open, though you can see the program running in task manager. (For example when I had to kill MC - or it killed itself - due to the problems I was having with G-Force mentioned above!)
If you look in the
services processes tab of the task manager (assuming you are running Win2k or XP and have this as an option) you will see a running service for MC. Sorry, I'm not at a Windows machine right now so I can't tell you the exact name, but it is something obviously related. If you end that process and then try to launch MC it should open up fine.
I believe what happens is that when MC crashes, the process gets "locked up" too, but does not get killed when you kill the MC GUI through task manager. When you try to re-launch MC it tries to launch or talk to it's process (which is not responding) and then can't launch the GUI. Of course, who knows if this is what happened to you (since you didn't mention MC crashing at all before this problem manifested -- maybe you didn't even know that it had)... But if you ever have a similar problem, I would look for and kill the process if it's running still. Of course, rebooting would solve the problem as well!