no sound suddenly in cubase 5

Suddenly my cubase5 has stopped working. i am using windows xp.when turning on my computer i get this message. the program could not start because mgsimcommon.dll is missing.
I have tried to reinstall cubase but nothing seemes to work.
when loading up my cubase the pc turns into security mode. Help! :smiley:

im not been very helpful here but try windows 7 ,i dont half the trouble i used to have with xp.of course whip out the hard drives with all your projects and audio on first