Can't provide a solution but the same thing happened to me a while ago when I deleted some Class Modules and I had to set up a new personal.xls workbook again. It may have been the deletion or it may have been something else, don't know exactly. I take it that you had not done anything? Just opened XL and Personal.xls was missing.
Some board members might have a recovery solution for any lost macros you had. Hope your stuff was backed up. Not sure why these things happen but there a pain. Hope you get it sorted soon.