Sometimes you can't access a WinXP computer after installing Norton Anti-Virus.
There might be a variety of errors at the other computer depending on the operating system.
On the XP computer, in the Event Viewer / System log, there will be the following error:
The server's configuration parameter "irpstacksize" is too small for the server to use a local device.
Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\lanmanserver\parameters
Edit the IRPStackSize
Give it a value of 15
Reboot the computer