Since the connection is shown in MercuryB, you're correct the connection get through - and possibly back.
When you get a blank page, and right click, to view the source - you should have something there - at least an empty head etc.
Secondly, a blank page could be the result of nothing to display (sorry that I'm not more familiar with MercuryB). I believe only public lists are handled, and if you have none - then logging in shouldn't be possible.
Other possible causes would be path settings that are not correct.
Kind regards / Peter