for about a week its been running smoothly but recently whenever i click the shortcut to run it my screen goes black like it normally does when opening the game but then it suddenly freezes with the timer mouse icon which i cant move about. I have left my pc at this screen for about 30 mins with nothing forcing me to forcefully hard reset my pc.

anyone know why its doing this?

Reminds me of this:

http://www.systemshock.org/index.php?topic=4617.0

Try out the solution mentioned in that thread and let us know if it works.