Okay, thanks for all your helpful suggestions people. I've tried deleting the cache, reinstalling, patching the unofficial patch, no wash. When I tried to start a new game it couldn't even load from the start, which is especially confusing. It suggests the area file on the CD is corrupted, yet I hadn't used it since i first installed the game at which point the mortuary worked fine. So the only thing left to try is the cheat codes, but everything seems to suggest the mortuary itself is a no-go area with my computer for some reason.
Thanks again, any more help would again be appreciated.