Hello everyone!
I was hoping to get some definite answers here about the problem i have been experiencing with this iBook.
To start from the beginning:
My girlfriend bought this iBook so she would finally have a good computer and be able to take it with her (read, she is a pc user and i'm trying to get her to switch

)
So what happened is, we got this on second hand and it was working fine booting normally ect.
Then i decided I would put in the hard-drive and dvd player of my dead iBook, because i thought 20Gb would fill up real quick and the dvd drive was faster.
So I took the iBook apart using a ifixit guide and put it together again, I didn't run into any issues during the process and was done within an hour.
But then when I tried to power it up it did nothing!
So assuming a cable came loose I took it apart again and found the DC-in cable was loose on the main-board. So I connected it and made sure it didn't come loose again during reassembly .
When i was done I pressed the power button and... nothing

I didn't understand, I did a lot of taking apart on all kinds of different mac's and pc's and this had never happened before..
so I put it away to have time to think and gather some information about what could be wrong.
After 2 day's I picked it up again, put it on my desk and before I started another internal check i thought i'd try the power button again.
This time it started!!!!
I knew there was some data on the hd i put in i needed so i booted in target disk mode and started to copy the data, the search and copying costed me about 2 hours in that time the machine worked fine.
When i was done i put in a 10.4 install dvd, shut the computer down and.... you can guess it didn't power on..
A bit stunned, I decided to take it apart again assuming there was something loose..
I checked every cable and connector i could think of, but found nothing..
Reseated all the cables and checked the pins weren't bend put it back together and as I expected it still didn't work.
My girlfriend has already given up hope but i want the machine to work!!
So today i picked it up again, pressed the power button and.. YES it worked again!
I installed 10.4 rebooted it a few times, put it in and out of sleep and let it run for a few hours in which it was working flawlessly.
To put it to the final test i turned it off again and after that it didn't power on like the other time..
So now I am wondering what could be causing this problem, battery is fine, charger is fine, resetting PMU doesn't help (i do see the charger light go green for a few second so it does respond to it) taking out airport and ram doesn't change anything either.
Btw. it is not effected by the common screen problem, its either completely working of not working at all.
I hope someone can give me a tip where to look for the problem..
Thanks in advance!