|Problems like you describe are almost always caused by a defective keyboard - stuck keys, or a cheap one that has been used a lot and has worn out some of it's contacts, or a corded one that has some wires broken inside it's cord. |
If that's the case, the keyboard won't work properly on any computer - have them try the keyboards with another computer, or try a third keyboard with their computer
Cleaning up the system physically would probably have no effect, but checking connections might.
They could try making sure the main connector from the power supply is properly seated in it's mboard socket.
It's extremely unlikely there'sanything wrong with the USB or PS/2 port, and even if there was, it's almost impossible for both to not work properly at the same time, unless the power supply is failing and is not able to supply enough 5v voltage or current - in that case other USB devices and CD and DVD drives won't work properly either.
Have them check your PS voltages in the bios.
See response 4 in this:
Of course, if the keyboard is a "combo" one that can be used with either a USB or a PS/2 connection, if it doesn'r work properly when connected one way, it's not going to work properly connected the other way either.
A USB connected keyboard may not work properly when connected to certain USB ports, but in that case it usually works fine or doesn't work at all.
See response 3 in this: