Network places on local computer become unknown

[Matthew]

I've set up a home network with a desktop computer, a
laptop computer and a router which connects to a cable
modem. Everything used to work perfectly until recently
I've found that the local shared resources in my network
places on my desktop computer have become unknown. I
arrange the network resources by computer(name) and show
them in groups. All network folders from the laptop are
grouped together under its computer name 'mobile' but
those from the desktop are grouped together under
the 'unknown' section as oppose to the desktop's computer
name 'desktop'. All the network shortcuts work perfectly.
It just bothers me that the desktop computer does not
recognize its own local shared resources while the laptop
also running xp home has no problem whatsoever.

I appreciate if anyone can help. Thanks

--Matthew