MN-500 Router or Vista

Here is the problem I am trying to figure out. I have a current setup with a
XP PC, DSL Modem, and MN-500 in one (main) room. In the other room, I have
another XP PC connected via an Ethernet cable to the MN500 (jack in wall of
other room and jack in wall of main room). Everything works. I replaced the
XP PC in the other room with a Vista PC. When plugged into the same ethernet
jack, I get a "Cable not plugged in" message.

If I carry that Vista PC into the main room and plug it directly into the
MN-500, it works. I tried the old XP PC and a Win 2K laptop on that jack in
the other room and they work fine. The Vista PC does not. I've changed all
the cables and no difference. Thoughts?