Deactivate Acrobat reader X pro form an unavailable PC

First of all, there's no such thing as "Acrobat Adobe reader X pro". There's Adobe Acrobat X Pro and there's Adobe Reader X.
Only the former requires activation, as the latter is a free application.

At any rate, if you don't have access to the computer you can't deactivate it. Just install it on the new machine and if there's a problem with the activation contact Adobe directly.