You never stated which win os is on the pc now and which win os was on their previously. If this is a PD9 retail version that is on the pc then all you have to do is to install it again. That would fix it and then you will be able to uninstall it after a reboot if you wish. If this is an oem version then use the restore disc or restore partition on the pc put it back in the original to the previous factory install and then use the windows to uninstall PD9.
There really is no reason I could think of to uninstall PD9 as it can co-exist with PD16 on the same pc. The full version of PD16 allows it while the Upgrade version require the previous to be removed. You save no money buying the upgrade version instead of the full version and it will cause you problems years later when you have to reinstall it for any reason as you require PD9 to be installed again or have the original license key for it.