Licenses of Adobe Acrobat XI does not work anymore?

Hi, the public body in which I work has bought 3 licenses of Adobe Acrobat XI in 2013. The licenses have been installed on three PCs. Now 2 of the 3 pcs are out of order due to motherboard failures. I would like to install the licenses that I can not use on broken PCs on 2 pc but it seems that the serial number does not work anymore. how can I do? Thanks.