I have an SGI Itanium Based Altix 450 computer. When attaching a mouse and keyboard, the mouse works - the keyboard does not respond when typing/logging in. I've tried other known good keyboards. Same response. I've checked connections. The connections are good. There are 4 ports on the Altix. All 4 ports yield the same response. Usually, a computer that won't respond to an inserted keyboard has a motherboard problem. Is there any other known reason why this computer responds to a mouse, yet doesn't respond to a keyboard?

Wild guess: input has been redirected so the primates at the datacenter don't monkey with the box.

Sorry I didn't notice this earlier. If a keyboard stops working (any keyboard according to you) the first thing to check is Device Manager. There are separate tabs for keyboard and mouse. If your keyboard tab is not coming up with a yellow exclamation mark then look to see what's listed there. If it's a generic MS driver then you can just uninstall it and then reboot to reinstall the drivers automatically. If its listed as your keyboard brand name then you would have to reinstall the drivers that came with the keyboard if you used them. I'm assuming your using USB since you mentioned 4 different connections, look for USB issues in your Device Manager or settings in the bios for USB keyboard. If your PC has at least one PS/2 connector you can try connecting a PS/2 type keyboard to see if that works (they can be had for really cheap). The USB drivers for USB mouse and keyboard are HID drivers (human interface device) and some boards actually come with an adapter for using a USB board in a PS/2 connection.