Zap the PRAM if reinstalling the OS didn't help. That pretty much rules out the possibility of stale plist files, so what's left is resetting the PRAM.
I can never remember the exact key combo, so I'm sure someone will correct me or you can google it quickly. Pretty sure you hold Command-Option-P-R at boot. So, either immediately after you hit the power button, or after you start the system in a reboot cycle, hold down those 4 keys. You should hear the boot chime once, and then the system will reboot again. Generally people recommend doing this twice, so on the third time hearing the boot chime you can let go and the system will start loading the OS.
This will erase a few of your preferences like mouse settings, but nothing vital.
If that doesn't resolve your problem, stick your Snow Leopard disc in the drive, and reboot holding down the "D" key. This will load the Apple Hardware Test diagnostics which will run a few tests that will catch some of the most common hardware failures. You can also remove the side of the case, and look into the system. On most models, between the two RAM trays, there's a set of LEDs. If you don't see them, that's good, but if you see any of them lit up, let us know which ones.
When I try to change the keyboard system preferences or the bluetooth system preferences, the 'application' locks up (Doesn't bring up any details, force quit gets out of it). I've tried leaving it for ages to see if it eventually opens but it doesn't.
This means I can't use any bluetooth devices or change the keyboard shortcuts.
It only happens on one of my otherwise identical Mac Pros; the other is fine.
Any clues as to how to repair it? I tried reinstalling Snow Leopard but that didn't help. I didn't do a clean install though as I'd rather put up with it than make a clean install work with all the apps etc.
Thanks in advance,