Solving the dual-monitor freeze problem

We previously noted an issue affecting users that have dual display set-ups, most prominently when used in conjunction with the GeForce 4MX. Typically when moving a window or another item between screens (but also under other circumstances in some cases), the system will freeze completely and will not respond to force quit commands or any other input.

Separately, but possibly related, we have been experiencing problem in-house with our Power Macintosh G4/733 (QuickSilver, only one display connected). Using an Apple Pro Keyboard and Mouse, the mouse movement would suddenly cease, and the optical light on the mouse would also turn off.

Temporarily, the problem was solved by moving the Apple Pro Mouse from the port on the keyboard to the USB port on the back of the Power Mac G4. The mouse worked for several minutes, but then the entire system shut off, apparently from power failure. Subsequent attempts to connect the mouse directly to the G4 produced the same result - complete system shut down after a few minutes. In fact, with the mouse connected while the system was off, no startup could occur. Connecting the mouse through the keyboard resulted in no functionality, but did not cause a system shut down.

Eventually, we replaced the Apple Pro mouse with a Kensington model, which worked normally.

While there at first appeared to be no connection between these problems, we have since heard from readers who have had a greatly reduced number of system freezes (in some cases it may simply be the mouse's ceasing to function) when plugging the mouse directly into the Power Mac G4 rather than into the Apple Pro keyboard's hub.

So it appears that there may be some type of electrical problem occurring when the mouse is connected through the keyboard that is somehow triggered by USB action across multiple monitors. Our in-house case, which did not involve multiple monitors, was obviously triggered by some other factor - possibly a defunct mouse.

Users have been doing other tests for causes of the problem, coming up with nothing. One reader writes "I've swapped out all DIMMs (one or 2 at a time), reformatted the drive and reinstalled the OS, run without third-party kexts, run without USB hubs, upgraded to 10.2.6, taken out third-party PCI cards, and removed third-party things from /Library/StartupItems. Regardless of what I tried, the machine would always freeze inside of 30 days' uptime, once in as little as 5 minutes, while I was still launching applications."

If you are experiencing this issue, try connecting your USB mouse directly to the affected system. You might also want to try temporarily using a different mouse.

Feedback? Late-breakers@macfixit.com.

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