I suspect it may be because of the existing installation. Try uninstalling that in the normal way, then run the MCPR cleanup tool listed under Useful Links at the top of this page, reboot and then try your installation.
If you have such programs installed as Malwarebytes or Superantispyware for instance, uninstall them temporarily in case they block things.
If the CD doesn't then give you two choices. open it in Windows Explorer, locate setup.exe and right-click "Run as Administrator".
Sorry, only just had a chance to look at this. I've done as you said and run the MCPR tool. Went into explorer, there isn't a setup.exe file, the only application files are Install, McItInfo, Riskscan, stinger and stinger64. Tried running install as administrator and it just tried to go through the internet again, not actully doing anything though.
If I try to go onto any help scrren is doesn't allow me to go to live chat, only gives me a phone number which is only available when I am at work, away from the computer and unable to make calls!
Try using a different browser to get into live chat or phone that number from work and ask them what you can do outside those hours other than chat, maybe they will be able arrange a callbacvk.