Hi and welcome
things to check:
Cables seated properly in both drive and
mobo-- also grunge can cause poor signal-- cables do fail, also
IDE controller settings in BIOS
Perhaps a new CMOS battery-- or just remove the current one and see if there are directions to reset your CMOS (bios customizations) if any.
Improper shutdown/power surge/brownout can cause bios issues.
Power supply-- try a spare connector-- if available.
Make sure the drive is actually spinning up. If it is--leave it-- if you open the case you should be able to hear/feel it.
Sometimes --for reasons known only to the computer gremlins-- just the act of removing the cable-plugs/re-inserting them can do the trick
Are you hearing any tiny "beep codes" when you start up ?
let us know