Mayi, I've confirmed that my HDD is working *phew!*, but the
computer has gone into a state of comatose. My IT friend was kind
enough to check for me, and he says it could be anything - power
supply, RAM, motherboard, or CPU, so we'll never know now.
Since the pc is 5 yrs old, I've decided to just buy a new pc
instead of trying to troubleshoot, as new parts may not be
compatible, anyway. Once again, many thanks for your help and for
sharing our pc concerns. 
