Power Mac G5 PPC crashes at start-up when any USB devices are attached

I have recently begun experiencing a fan noise issue with my Power Mac G5 PPC Quad (Late 2005) running 10.5.8. During regular use the fans are constantly running and can get rather loud. Sometimes after my machine had been on for a while (a few days) it would crash and the fans would go all the way up in volume, like a plane engine. Trying to restarting it normally some sometimes get as far as the grey screen with the apple logo before the screen would freeze, the fans would kick into high gear, and two red LEDs in front of the RAM slots would come on. Other times I wouldn't get as far as the screen, but rather it would crash soon after the start-up "bong." To remedy this issue I would have to unplug my USB devices, start up the machine, and once I got to the login prompt, plug all the USB devices back into the machine. Other times I would try to boot several times, and would end up zapping the PRAM, taking out the CMOS battery and putting it back in, etc.

I noticed that a red LED between the first and second RAM slots was always on when the machine was on. Doing some research I found that it was an indicator of an overheating issue. One suggestion was to boot the machine from my OSX install disc with the diagnostics (hold down "C" at startup), or at least boot the machine, get in and run a disk check to make any permissions repairs/start the process for figuring out what is causing the problem.

However, when I tried booting into my machine with my OSX install disc and just the Apple USB keyboard that came with the machine, the machine crashes since there is a USB device attached.

So my dilemma: How do I boot my machine from the OSX disc without using the USB keyboard, since it makes the machine crash at start-up? Or how do I repair any permission issues on the system drive since you can't repair an drive you are using to run the operating system. Any ideas why this is happening? Ideas on how to fix it?

The one time I wish these Macs still came with the old school keyboard jacks...

Thanks