I know it's probably a silly question, but I have to ask anyways. I just dug an old Powerbook 100 out of a friends basement and looking it over I can't find out how to turn it on. I've checked online with no answer forthcoming, so my question is this. What is the magical button that will make this strange grey box power on?
The powerbook 100 has a reputation for not operating for more than a moment if its main battery is dead, even with the power adapter is present. Your mileage may vary.
Typically hit the space bar if I recall that was what was recommended in the manual.
There is a switch on the back that disconnects the PRAM batteries which are most likely dead. The main battery is also most likely shot as well as they were sealed lead acid batteries and didn't take kindly to being fully discharged.
If the battery is still installed try removing and see if it will start, you might try flipping out the PRAM battery holder as well.
Be very careful with the AC adaptor as there was a recall on these things. The original had a plastic tip that cracked after a minimal amount of use and this would short out the soldiered in fuse on the motherboard.