Firstly, calm down, if there was nothing on there to lose, then you shouldn't stress so much yet, and you don't know what the fault yet (I know it's gut-reaction to think the worst, but try not to). Even if it is your HDD, at least you've lost no valuable data, and they are fairly cheap to replace (despite the recent increase in prices) and this is the perfect
situation to find out your hard drive is dying - nothing worse than finding out when you have data on there (that may not have been backed up for a while/ever lol).
Initially, whilst the click HDD is not a good sign, it could also possibly be that the DVD disc is goosed. Does it have any scratches or is it pristine? How old is it, is it original, or is it a copy?
Do you have any old Windows/Linux discs, or access to a DVD burner?
Let's take it one step at a time, plenty of us on here will be able to help you don't worry.