Q: USB ports not working

Was setting up my old PowerBook G4 Alu. 1.25GHz to be used by my son as clamshell w/ external display & keyboard.

Apple keyboard attached to the left-side USB port : everything OK.

Then, I switched the keyboard to the right-side USB port, to connect a webcam to the left one.

Boom : all gone. USB ports not fonctionnal any longer.

Did all checks, eg. System Profile : both ports are recognized, every device connected to each is recognized, LED devices are lighten up, etc.

Then, did all the power management tricks found on the forums : PRAM reset, Power Unit reset, battery off, all-night unplugged, etc.

Still, nothing works. USB ports still off.

Any idea, before I click on "purchase a refurbished Mac mini" ?

Thanks in advance.

_Marc