why can't I watch movies on my iMac that I have purchased

I have been on my computer (iMac) for over an hour getting the run around.

I have movies on my iMac in my iTunes and when I clicked on one, it asked to authorize this computer to play this....so I did, and then it says another Apple ID, so I have it send me a link to reset my password since that link is not working....

Can't watch the movies I have down loaded onto my iMac...any help....no more run arounds please