I'm sorry but it seems that your flatmate most likely has got a bad hard drive now. Reformat will not help. Data recovery may be possible, but specialist help will be required for it.
I've dared not to keep a record of all those Ph.D. theses, seminar works, publications, and sundry material related to the above that I've seen having been offered to the gods of the deep Hard Drive Forest, it would only make me feel like I'm banging my head against the wall all the time.