"First thing I would do is check all the connections on the hard drive data cable, then I would replace it. Here's the cable: MacBook Pro 13"" Unibody (Mid 2009-Mid 2010) Hard Drive Cable
Here's the installation instructions: MacBook Pro 13"" Unibody Mid 2009 Hard Drive Cable Replacement"
the problem is in fact the SATA connector at the tip of the cable. It only makes good contact with some HDDs. the fix! is simple.
put 2 lines of masking tape on top of the DATA side of the HDD connector, then plug in the ribbon cable and turn on the machine. you will get the apple sign if the HDD has OS on it if its empty boot from cd and check on disk utillity.
putting the tape:
instruments: masking tape(blue or white), a small flat screw driver, and scissors.
put a piece of tape on top of the DATA side or if you want it could go accross the DATA AND POWER, NOTE, ON TOP OF THE PLASTIC AREA, DO NOT PUT TAPE ON THE PINS SIDE, I REPEAT DO NOT PUT THE TAPE ON WHERE THE PINS MAKE CONTACT. THE TAPE GOES ON THE UPPER SIDE THAT IS ONLY PLASTIC. cut tape very close to the edge. make the division between DATA AND POWER on the tape and plug into ribbon cable.
The tape goes on the hard plastic connector (that connects to the drive) at the end of the cable. You want the tape to reduce the inner space so that it forces the metal pins to make better contact, being careful not to place the tape over the metal pins themselves else you'll have no connection. I basically inserted the end of the tape strip into the thin slot of the connector, than wrapped around a couple of mm onto the outside of the connector.
**BUT** while the trick allowed me to finally see the drive from Disk Utility, I never got it beyond that. In the end I purchased a replacement for the cable and the problem was solved.