I have the same problem ...... every time I try to download it this message comes up (being going on for months now, luckily I have another program SerifPhotoPlus to use in the meantime) ... my computer is installing other programs quite happily ...
" Setup cannot continue because a previous installation requires your computer to be restarted. Please restart your computer and rerun Setup"
I had the beta version installed so I uninstalled that. Still the same message comes up ... again and again despite days of restarts ...
I'd appreciate your help please .......... thank you :) (I really cannot do a factory reinstall etc as suggested above)