Can't install photoshop CS5 on second computer

When I try to install CS5 on a second computer it askes for the CS5 serial # and next wants the serial of an upgrade or gives the option of installing a trial.  I contacted support who said I only showed one active CS5 which is on my old computer.  They gave me two web addresses to try to install the new copy.  Neither address worked and gave me "not Found"  I tried on both Chrome and Firefox in case one was the problem.  I need both copies during the transition from the old CPU to the new one.  Support told me to ask the Forum  for help.  Both CPUs are Dell and run Windows 10.  I get the software from the origional disc and not from the web.