I'm trying to fix an older model MacBook Pro (A1150). One day it just stopped booting past the blank blue screen. I realised the battery and PRAM battery were both dead, and thinking this was a likely cause replaced them both. Now it boots past the blue screen, does the progress bar up to 100% but doesn't move past that screen. Just sits there with the progress bar full. It also gets quite hot around the number keys, and the fan is on (quietly) which is odd considering it's not really processing much. I've tried zapping the PRAM a few times, and resetting the System Management Controller (SMC) twice. I've tried conncting a bootable drive, but when I hold down option on startup I never get the menu of which drive to boot from. If I use the broken MacBook in target disk mode I can see all the files, so I know it's not a HD failure. Any more suggestions?