No Self Ping

I have one workstation on a Workgroup that was working fine until an update was installed. Now it CAN access internet through a router – but CANNOT access any other local Workgroup resources (says network is inaccessible). Can ping the router – but NOT any other workstation in the workgroup and NOT own IP address. Loopback address (127.0.0.1) DOES ping. It is running XP Home – all other workstations running XP Professional.

Tried reinstalling network drivers – same behavior over wired and two different wireless network adaptors.

Is the TCP/IP stack corrupted? Have tried to reset the stack as here: http://support.microsoft.com/default.aspx?scid=kb;en-us;299357 but no effect.

Any suggestions welcome!