Cisco 2600 VPN issue

At my work, I've got a Cisco 2600 Router configured for VPN access. It was all configured before I took this position. Now, randomly, it decided to act up.

I can use XP's VPN connection and it connects just fine, but I can't browse any files on the remote network or connect to any devices. I can ping their IP addresses however.

I've used several VPN usernames and passwords, each which could previously have access to the network and I haven't changed any settings. Since I'm not super familiar with Cisco routers, where would I start to diagnose the problem? I did a simple reload but that did nothing.