D: drive missing

Dear Friends,
I am in a critical situation, please guide me, Actually its happened in my office desktop, I try to install partition magic just to check whether it is working with windows vista or not, because i had an old version, then later I found that My D: drive is vanish from my system, I am using windows-7 in my office PC, all my work related data saved in D: drive only , I don???t have any latest backup. I don???t know what to do, actually I am dealing with lot of Engineering drawings which I saved in partition D:, if somebody can help me, will be a great deal.