Internal hard disk drive not found

My friend is getting "Internal hard disk drive not found. To resolve this issue, try to reseat the drive". I've done this (compared to her I am a technical wizard so you can imagine how computer illiterate she is!) but it hasn't resolved the problem. It's a Dell Inspiron 1525. I've also run the onboard diagnostics, again without success. Do you think her HD is knackered? I don't know if you remember, but I have the same model and my HD had to be replaced a couple of years ago.