Forgive me for asking this but you are running as admin and you have turned off UAC?

If so don't give up. Do what nov2011 suggests and do a complete unintall. Then as admin with uac off reinstall, but this time do not do the trial install, just use your product id and serial from the start. Maya should auto activate the first time you run it.

What os are you running? When you tried the 2012 install were the missing files part of the isntaller or windows system stuff. I am concerned that you are getting corrupted installers or that you have system issues.

Did you actually get the trial installed and running at some point?

It should run as a trial, fully functional for 30-days. Once it runs you know it's not the maya installer itself. If activation fails after a successful install then I would suspect there is a problem with your product id and/or serial.