No expert here, but I know I am among them.
I took out my HP desktop's secondary hard drive, a Western Digital 400B, and put it into an older computer whose hard drive and floppy I had just destroyed - or so I believe. Again got the message 'Primary hard drive fail' for the Western Digital as booting. Whether this is my fumbling of a cable or I've really fried things I do not know. But am wondering if it is safe for my HP to reattach the 400B into my HP and try to examine it, and possibly work on it, from there? (Or could I be asking for trouble just by trying this?)