About twice a day, my mouse and keyboard both stop responding to input (e.g. pressed keys, clicked mouse buttons and mouse motions). My screen continues to update normally (the clock advances, etc.). When this occurs, I've found that I can take the USB cables for my mouse and keyboard out of the USB ports on the back and put them into the USB ports in the front, and they become responsive again. If I try to put the USB cables into the back again (after the back USB ports failed), they still do not work. After some more time (hours sometimes), the front USB ports fail and then I have to hold down the power button until the computer turns off and then I reboot, and the keyboard and mouse work fine.
After installing the proprietary ATI/AMD FGLRX video driver, the problem seems to have decreased in frequency (from failing every 15 minutes, to failing every 3-4 hours).
Computer: HP Compaq 8200 Elite
Keyboard: USB Microsoft Natural Ergonomic Keyboard 4000 v1.0
Mouse: USB Logitech Mx510 Optical Mouse
Video: dual Dell P2411H monitors with a resolution of: 1920x1080@60 Hz
Proprietary Drivers: ATI/AMD proprietary FGLRX graphics driver
I thought it might be Unity so I installed XFCE and ran that instead for a while but that but it did not help prolong the responsiveness of my mouse and keyboard.
% uname -a
Linux timbuntu 3.0.0-17-generic-pae #30-Ubuntu SMP Thu Mar 8 17:53:35 UTC 2012 i686 i686 i386 GNU/Linux
% lsusb -vt
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/3p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/8p, 480M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/3p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/6p, 480M
|__ Port 3: Dev 3, If 0, Class=HID, Driver=usbhid, 1.5M
|__ Port 3: Dev 3, If 1, Class=HID, Driver=usbhid, 1.5M
|__ Port 5: Dev 5, If 0, Class=HID, Driver=usbhid, 1.5M