Startup Disk HDD not recognized... fix/alternatives?

Hi all -

I have a macbook pro 2GHz Core Duo that I recently purchased... knowing it was having trouble booting from the internal hdd. After removing the logic board, cleaning it, reseating, etc... I got it to boot up to the hard disk twice and then it went back to only booting from the optical bay or an external hdd.

I'm assuming this is a hard drive controller issue, correct? Any suggestions? I know I can remove the optical bay and install the after market hard drive bay, but if I want to keep my dvd drive, are there any fixes? I did note that all the pre-unibody macbook pro logic boards have an unused port site to the left of the optical bay but before the memory opening. Is that a potential site I could link some "X" cable to?

Thanks

PS - I tested using both another HDD and another HDD flex cable