Few times ago,I have had some troubles with my powerbook G4.
It blocked, or didn't open....with awfull messages (Panic Kernel) or sometimes the famous message "you need to restart your computer.....blablabla (Kernel Panic).
With a panic.log file, with "extension" line....but how difficult is to understand this "langage" for me.
So..after check on the web, restart my computer with different reset (see appel assistance), i supposed it was the PRAM battery (my computer is about 2002) or my memory 1Gb.
So for me my computer's trouble were: PRAM battery + Memory 1Gb were out of order.
For the PRAM Battery, i used the very well guide
For the memory.....wait to have some cash to buy a new...
About replace PRAM Battery :
No more advice....Guide is very simple, well done, and detailed.
About the trouble kernel panic: firstly try simple things..and pray !
About Ifixit: Very Very good site. Have no trouble since i used it to understand how to do or when i bought tools or products. Used it for ipod, G4 ibook ou G4 powerbook.
Shiping from US to Europe very quickly