Massive problems...please help.

I have a Win2k desktop and a Win XP laptop (wireless)
connected to a Linksys WAP, DSL/Cable router with a 4-port
switch.

When I first set up the network I had internet connection
on both machines, the XP machine could access the 2k
machine, but the win2k machine couldn't access the XP
machine. After making sure the appropriate folders were
shared, same username on both and running the Set-up home
or small business network wizard I was able to get both
machines to communicate with each other...but then I lost
my internet on the XP machine. After trying to get
internet connection back up, I lost all communication
between computers. Can't ping each other but when I do an
ipconfig /all everything seems normal...both machines are
on the same network/subnet they both belong to the same
workgroup and I have XP's firewall disabled, only running
TCP/IP, and I have Net BIOS over TCP/IP enabled on both
machines. One minute I can ping each machine the next I
can't. None of the Wizards will solve the problem I'm
having.

Don't know what to try next..thank you.