Mac G4 display/trackpad issue... running 10.5.8... 10 seconds after normal startup screen, screen suddenly goes to new lower resolution, desktop expands beyond screen boundaries, and trackpad movement moves not just cursor but also desktop content...??

When you first boot the computer reset the PRAM/NVRAM. The PRAM stores info about various functions of the computer, including screen resolution. Give that a try, you may also try plugging in an external monitor and see if that doesn't correct the problem. If the problem persists you should have the laptop looked at.

Good Luck!

Some models of portable Apple computer have a PRAM battery, so after some duration passes those may require a battery replaced; it is on the logic board and requires a service visit to replace. Not all portables have one, some may have a capacitor or other charge holding device, and would get power from the main battery or household mains by adapter.

But as advised, the PowerBook should see a trained service expert that would know about these things to determine the cause and suggest a possible cure; also an estimate based on some testing would be helpful. Some companies take repairs through the mail or an express parcel company, and arrangements may be made ahead of shipping to be sure of what services, costs, and other details are to be attended to before sending.

Perhaps the suggested reset of the PRAM and/or Power Management Unit (PMU) may be considered.

Good luck & happy computing! 🙂