Why does my MacBook only start when pressing 6 and 4 keys?

I have this lovely little Macbook 1.1 that only responds to a startup when I hold the the power button down for 5 seconds and then tap the button again while pressing 6 and 4 keys down (for 64-bit mode) or in Target Mode. Safe Mode is not available.

My vintage laptop took a bellyflop on a basement floor as I was on my way out the door for a road trip.. The machine was in Sleep Mode when it fell . When I opened the cover, the screen returned, but I got this little Mac "ditty":three tones followed by two tones and then another three tones. I shut the laptop down and restarted it and it booted with the same pattern of notes played again. I restarted again in Safe Mode and it booted OK. I shut it down and reset the NVRAM and the notes stopped playing on startups which was reassuring. I was able to get it going in Safe Mode for several more restarts, but after two days, the Macbook stopped recognizing Safe Mode and I began to receive Kernal Panic Warnings at startup ('unable to find ACPIPlatform'). I reinstalled the OS using Target Mode. but there was no improvement. I reset the NVRAM again and reset the SMC. It booted normally once and then resumed its fickle dormant state.

I put it in Target Mode and tested and retested the hard drive and the drive passed OK. I did a RAM Check (with memtest) and and that was OK. At that point, I noticed that the machine was not shutting down properly and was depleting the battery. Suspecting the SMC, I did another SMC reset which didn't fix things.

Now here's a funny thing: after much trial and error, I found that I can often restart it after an SMC reset by holding down the 6 and 4 keys. I understand that a Core Duo is not a true 64-bit system but, still, my little startup trick works (more often than it doesn't) . Once started, my trusty MacBook works 'Just Swell' - like the Olden Days- all applications opening etc. But once my hard drive goes to sleep, or, I shut her down. I'm back to square One : SMC reset and hold down 6 and 4...

Does anyone have any ideas about curing this bug?? Is it the SMC? Could it be that somehow the one of the cores of the CPU that is involved with startup is damaged?

I took it in to see the Mac 'Genius' and he was at a loss. very disappointed there.

Well, I have tried the external boot and the MacBook hard drive booted up fine. So I don't think the drive is bad. I also turned the AirPort off followed your advice to check the battery and the battery is OK.

Also, I reset startup to safe mode using the Terminal command, but it still wouldn't boot into safe mode. I then tried the sudo NVRAM command to set it up for 64 bit mode to see if I could skip the ritual of pressing the 6 + 4 keys, but there was no change - still had to press the keys! I noticed that the sleep light is not glowing when the lid is shut. I checked the sleep settings, but they were set up correctly. I am baffled.

Now I'm wondering if pressing the 6 and 4 keys has some effect on the start up other than setting up the 64 bit kernel. After all, the macbook is a Core Duo (not a Core 2 Duo) so it doesn't accept the 64 bit kernel, right?

Kevin