Mini Display Port & HDMI problem

kelbal

Hi.
My laptop has a Mini Display Port, and I have an adaptor to turn that into HDMI female. This all works fine on my TV at home, connecting my laptop to HDMI. However, my work has lots of projectors I need to be able to connect to, that used to be VGA only. Some work was done recently to make them HDMI compatible, and in many locations there's a little white HDMI box on the wall. Other people with HDMI ports on their laptop can connect into this fine - but me with my MiniDP and adaptor, can't get a signal - but like I said, this setup works fine at home on TV. Any ideas whats going on?

Thanks in advance