Posted before thinking it was the router, but this was not the case, and wondered if anyone could help....

I have 2 systems running XP Pro. I did have a working network, for file sharing, but hav'nt used it
for file sharing for a while. 1 system is a desktop, the other a laptop. Both can access the internet fine,
with no issues. Tried accessing the printer from the laptop this week, and found all file sharing had failed!!
I have tried everything I can think of, uninstalled ZoneAlarm, checked the net guest account is active, Checked in the group
policy editor, that the guest account can access the network, and is not a member of the deny network access, although the guest account
is in the deny logon locally, but every time I disable this, the guest account itself becomes active.
Both PCs have static IPs, and both can ping the router, but not each other. The laptop is wireless to the router,
the desktop is connected via homeplugs to the router. The previous setup that worked, was both systems were wireless
but I have moved the desktop to the attic room, and wireless was a bit iffy.  Occ I can connect to the laptop from
the desktop, mainly when the laptop is on, but no-one logged on. It seems that as soon as I login to the laptop
all filesharing and networking failed. Desktop is never accessable anymore. Same username and password
on both PCs.  Even resorted to using the home networking wizard, to see if that would resert any iffy
network settings, but no joy.  I am really stumped now, and unsure as to where to go next.  It used to work with no setup needed
at all really.  Can anyone offer advice.

I find this very odd.....  Zonealarm been uninstalled on both systems, windows firewall disabled. Still both systems refuse to respond to a ping request, but they can ping the router OK. What could block pings other than a firewall??  This is frustrating the hell out of me.....

Result of an ipconfig /all on the laptop.....  I have re-enabled DHCP...

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\Chris H>ipconfig /all

Windows IP Configuration

        Host Name . . . . . . . . . . . . : excelsior
        Primary Dns Suffix  . . . . . . . :
        Node Type . . . . . . . . . . . . : Unknown
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No
        DNS Suffix Search List. . . . . . : lan

Ethernet adapter Wireless Network Connection :

        Connection-specific DNS Suffix  . : lan
        Description . . . . . . . . . . . : Atheros AR5004G Wireless Network Ada
pter
        Physical Address. . . . . . . . . : 00-11-F5-44-33-3A
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.64
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.254
        DHCP Server . . . . . . . . . . . : 192.168.1.254
        DNS Servers . . . . . . . . . . . : 192.168.1.254
        Lease Obtained. . . . . . . . . . : 11 November 2009 11:31:14
        Lease Expires . . . . . . . . . . : 12 November 2009 11:31:14

Ethernet adapter Local Area Connection:

        Media State . . . . . . . . . . . : Media disconnected
        Description . . . . . . . . . . . : Realtek RTL8139/810x Family Fast Eth
ernet NIC
        Physical Address. . . . . . . . . : 00-02-3F-8F-19-60

Are you pinging by name or ip-address?
One option to try is to enable netbt on the network services on both machines. I used to have to do this on some XP machines a few years ago.

Pinging by IP. No software firewalls at all.
A bit concerned about the Node type being unknown.....

It might be that zonealarm has "knackered" it.
Delete the interface and do a hardware scan, then see what it says.