computer can't detect primary master/slave

I'm having problems with my computer which was running okay until I shut it down a couple of days ago (previously hadn't been shut down for around a month)
Now when I try to start it up it cannot detect the IDE primary master / primary slave although it can detect the secondary devices. I get a message saying disk boot failure insert system disk and press enter
Have tried taking out the battery and connecting hard drive to another machine but with no success
Can anyone out there suggest anything? I have a lot of work on the hard drive which I haven't backed up - the computer is old and no great loss so I'd settle for just been able to retrieve the work
I've read about flashing the computer and am willing to give anything a go so long as the procedure is explained in very very simple English as I'm not a computer whizz

 

I think your harddrive is done. I think if you took your harddrive into a computer place they would be able to retrieve your work.