I'm not sure what the "hat" you're referring to in the topic is, but if a hard drive stops being detected, that's frequently a hard drive well on its way to the afterlife. The challenge with hard drives that are dying isn't fixing them -- they're very rarely repairable -- it's recovering any data that you didn't back up before it gives up the ghost (sadly, many people house crucial files on their hard drive but have no backup plan).
Now, if you think the hard drive is loose for some reason, the obvious next step is to check the connection. If you still can't get it to detect, it's time to remove the hard drive, put it in an enclosure, and attempt to read it on another PC.
Anything more specific, I think you're going to have to be a bit more clear.