Hard Disk failure

My PC occassionly switches to that blue screen and displays the following error ” cannot write to c:” and the system hangs and I am forced to reboot. I suspect my network card, but I don’t think that’s the problem. I also added more RAM to take from64MB to 128MB, still to no avail. Could it be that my hard disk damaged? I also reinstalled my Win95 and still no change.
It does this weather you are working in any application or while nothing is running at all. Can you help.