how to clear pram in mac pro a1398

Can you be a little more specific as to the steps you are taking that lead up to you seeing "Your computer is Disabled"? The reason I ask is because the only time I have ever heard of a Mac becoming "disabled" is by typing in the incorrect EFI password too many times, similar to what you see with iPhone and iPad. Also to clear PRAM and NVRAM (I forget which of the following two resets which, so I just always do both to be sure): Hold Command+Option+Control+Shift with your left hand and press the Power button for 5 seconds; Hold Command+Option+R+P and then Power on the device, keeping all keys besides power firmly held while the device boots. The device will power on and then instantly reset if done correctly. Sometimes I've had to take a ram stick out, and other times I've had to use ram from a different computer entirely, so if for whatever reason you just can't seem to get it to reset then switch the ram and try again.

I agree, I think clearing PRAM will resolve his issue. It sounds as if he removed the EFI password and is getting prompted with an iCloud lock at boot. The disabled information message is due to too many attempts.