I use a Dell Optiplex with XP Pro SP2 at work. It is on a 25 node LAN using W2k3 Server R2 SP2 with Active Directory. Recently this PC has begun to lose internet connectivity but still keeps LAN connectivity. All PCs are identical configuration: IP: 192.168.1.x; Subnet: 255.255.255.0; Default Gateway: 192.168.1.fixed. I can ping all objects on the LAN but cannot ping the gateway. All internet connections go through the same router ports.

Previous episodes were resolved by rebooting the cable modem and/or router and/or rebooting one of the DCs. Rebooting the DC should have no effect on the internet connectivity of any LAN object, but for some reason seems to work when all else fails.  This time, nothing has worked, including system restore. BTW: all system restore points except for the most recent have been lost.

Virus and other malware scans (multiple vendors) reveal no infestations.

I am perplexed; can any one enlighten me as to what to do now?

Thanks.