Virtually any system should be able to read PDF files....
Did you install v5 over another version? could be as simple as a .DLL file not being upgraded along with the rest of them.
May well be worth uninstalling ALL versions of Adobe Acrobat on the PC, Rebooting, Downloading the latest and re-installing.
I would not re-use the version you have just in case that one has a bug (or something odd!) in it, hence my suggestion to downloaded the latest.
Gary.