I spoke to a guy at MacSupport this morning and told him what had happened and what I had tried. I hadn't reset the PRAM because I was unsure it needed that but he assured me it was worth a go so we tried and nothing. Basically it needs OS X reinstalling (my next step lol) and I can retrieve my files my starting up in a different mode and connecting to a friend's macbook. Hers will recognise mine as an external hard drive and I can save all my stuff
Going to try fixing it on Sunday. I think it's the end of my study though...this was the last straw...