Sometimes things go goofy when you're working in a remote session (in PSSTERM, etc.), and you are unable to quit a program. The usual key combination (CTRL + ALT + DEL) will not work to force quit since the problem is not on the local machine.
However, a slightly different key combination, CTRL + ALT + END will work. Just choose Task Manager on the window that pops up, choose the program that you are having problems with and choose End Task from the choices presented. You may see an additional dialog box and have to "Okay" actually closing the program.