Parallels quits on opening?

Hey guys, my Parallels program cannot be opened, on launching it just quits everytime. It's a mystery to me as it used to run fine, I don't use it often and can't think of anything which I may have done to affect it so does anyone have the same experience or have any suggestions as to what the problem or solution might be?????

Does it give you an error message when it quits? Have you tried reinstalling it?