It is unclear what you mean by "Can I fix it?".
"Is the actual problem with this iBook G4 something that can be fixed by replacing hardware?"
Most of the time, people who see this particular symptom -- a blinking question mark folder -- have perfectly functional hardware.
If you are lucky, you are one of those people.
If so, you can fix the real problem, that gives this particular symptom, without any hardware modifications.
Have you tried the ways of fixing this particular symptom described at:
If the real problem is one of the above software issues, then replacing perfectly good hardware isn't going to help.
If none of these fixes work for you, then it is almost certain that yes, it is a hardware problem that can be fixed by replacing hardware.
"Is the actual problem with this iBook G4 something that can be fixed by replacing the logic board?"
There are several pieces of hardware that, should they fail, would cause this symptom:
- bad hard drive cable
- good hard drive cable, but somehow it has come loose and needs to be firmly plugged back in.
- bad hard drive -- Is it possible that maybe your "new" hard drive is a dud and never did work?
- bad logic board
If the real problem is in some hardware other than the logic board, then replacing a perfectly good logic board isn't going to help.
"Can I fix iBook logic board by replacing or adjusting parts on that logic board?"
Not in any cost effective method.
There exist people with the manual dexterity and electronics test bench equipment and soldering rework station equipment to do that.
But there are far more valuable things they could be working on.
It's far more cost effective to discard the bad logic board and replace it with a good one.
"Can I fix an iBook G4 by replacing the logic board?"
Yes, if the problem is in fact the logic board, there are some excellent diagrams at
iBook G4 Repair
describing how to get at the logic board, and
Josh Calvetti Possible to Swap Logic Boards?
says he was able to fix an iBook G4 by replacing the logic board.