I use a D-Link 200

Question

I use a D-Link 200 modem for my broadband connection. For the past two days I have been able to establish a connection to my ISP but can't get onto the net. I called my ISP who had me uninstall and reinstall the modem. Now I find every time I switch my computer back on I have to uninstall the modem and reinstall it otherwise I'm back to my original problem of being connected to the ISP but not being able to get onto the net. Is it my computer or the modem that's causing the problem? I have XP on my computer.