Could you expand what you mean by "I do have a administrator account on this PC". - Do you mean you have enabled the Global Administrator account?
But. One suggestion, open Msconfig - Tools tab, and "Launch" - "Change UAC Settings" See if this satisfies your requirements. UAV is a text warning only, and if you are satisifeid that you can handle breeches into youer security, fairly useless.
If you do not have the "Global" Adminstrator account enabled, post back and we will toell how to go from there.
I'm afraid this does not have a lot to do with your black screen, but maybe we can deal with that as another issue