Usb Problem On Apple Cinema 22", USB Crash inside the screen Options

[sam7]

Has anyone ever heard or experienced a problem with the USB inside the Apple Cinema 22 flat screen? It's a 3 years old one to fit the AGP G4 port.
Mine has a serious problem, the mouse and keyboad that i had plugged into the usb sceen plugs froze, then i had a black screen.
i unplugged the screen transformer , the screen was back then i plugged the keyboard & mouse directly into one of the the G4 back plugs and it worked.
the screen works , only as a screen, which is the most important thing, but it sounds that the USB inside has burned, there was a kind of smell that reminded me of the good old days
with marshall amps transformers.
i changed the processor a few months ago from a G4 400 i moved to a Fastmac 1.4 giga, don't think it could have something to with that though.
Any idea or suggestions about all that?
Thanx for your help.