Using optical drive for boot I have an old MBP that refuses to see the HD in its normal slot , but I can boot from an HD in the optical drive slot using OSX 10.6.8. So far so good and it runs quite fast enough for my use , but if I put it to sleep it won't wake up. It won't respond to the power button either on a press or a hold. I have to power off and remove the battery to start it up again, and then it starts, switches itself off and then starts again and chimes. I have tried replacing the hall effect sensor for the sleep switch but the result is the same. One guess is that the computer needs to switch on the HD first and then the rest of the system follows on and without the HD in the main slot it hangs. Anyway , anyone else experienced this or can think of a solution?
My first thought would be to try and resolve the initial issue (i.e. the fact your MBP is not recognising the main drive slot), as that's what is most likely causing your current problem as well.

However, since you seem happy to work off the optical drive, I would try the following:


First reset the NVRAM and SMC (in that order)1
Boot up from the optical drive slot
Go to Apple > System Preference > Startup Disk
Ensure that the current boot drive is selected
Exit System Preferences and Restart your MBP


Now test to see if that has made any difference.

1. Since you haven't provided details of your exact MBP model I've included links to Apple's instructions. Make sure you read these carefully so that you're following the correct steps for your MBP.