Remote Desktop Connection woes... black screen with Earthlink ADSL

ok, here's a fun one, and I could use some help!

I have 2 laptops
1 mac and 1 pc
I have Remote Desktop Connection on both of them
when I try to connect through my home dsl, I get a black screen. But if I
bring either of the laptops to one of the multiple outside coffee shops... It
works perfectly!

I've tried a bunch of things at home including
1 connecting directly through dsl modem, skipping router
2 using router with laptop listed as the dmz IP
3 forwarding port 3389 directly to the laptop

nothing seems to work,and I just get a black screen

any idea?
I even tried (or think I tried) setting the mtu size... b ut it didn't seem
to work either

thanks!
-Josh