weird connection problem between domains

[panda]

I have two domains that are physically linked. However they no longer seem
to see each other (either ping or anything else). The first server (and
domain) called A is win2k, it is connected to the second server B (NT4) via
2 switches. we know the physical link is ok due to cable and ping testing
using a laptop. server A can see the internet router that is also attached
to the switch nearest server B. none of the clients on server A can see the
internet. If a laptop is placed on the switch nearest server A (switch A)
then the laptop can ping to server A but not server B. If it is placed at
switch B it will only find server B. the only time that the laptop could see
both networks was when i plugged it into switch A then directly into server
B. does anyone have any ideas what is happening here?

many thanks

sam

 

[panda]

A router between the two networks? VLANs?

The router is used by both networks to access the web, it is off switch B,
and can be seen by server A and B.

sam