can't see other computers on home net

I've got a laptop that accesses the internet just fine but can't see
nor be seen by other computers on my home network.

The laptop is running XP as are two other computers on the net and one
is running Win2K. All other computers can see each other without
problem.

I did not always have this problem. In fact, at one time, I configured
my desktop (XP) to map the laptop on startup. The laptop icon on the
desktop machine now has a large red element (not a good sign).

The laptop shows up under the workgroup on the desktop but I get a
permissions error when I attempt to select it.

FYI, I use the same user ID on both the desktop and laptop.

Any thoughts would be greatly appreciated!!

David