USB device error message

I have a G4 Cube, 500MHz, 60 GBs. I have an apple studio display 17in
monitor, an apple pro keyboard and an apple optical USB mouse.

I have had intermittant problems with the cursor freezing which is
sometimes solves by plugging the mouse into the left hand USB port. My
keyboard is plugged into my monitor. Sometimes I get this error
message:

"The USB device "Hub in Extended USB Keyboard" can not operate
becausse it needs more power than is available.To correct this
problem, you can :1)plug the device into an electrical outlet if it
has a power cord
2)Unplug the device and plug it into another USB port on your
computer"

The problem does not appear if I plug my mouse into the USB port on
the Cube.

Does this indicate a problem with my mouse, keyboard or montior?
please let me know if you can help,thanks