Remotely Logging in to my Windows Admin Account

I used to be able to remotely log in to my administrator account  on my windows PC from an IMac. 

I'm no longer able to do that. Now, from my IMac, I'm able to see my windows machines desktop(which I usually run using a Standard windows account) and open folders, etc, but when I try to log in to my Admin account, it doesn't work - The login page does not show up when I click on it. Or even if I try to open something that requires an administrator password, I'm not able to type my admin username and password from my IMac remotely.

Any help would be appreciated.