Logging onto Network

Hello, I am having problems logging onto the network. I have a laptop with Win98 on it. Now when I used to log on it usually prompts me for a username and password and it name of the domain server at the bottom. But now when I log in it goes straight to windows, without the prompt of the username and password. The machine is detected on the server because I can retrieve email. The TCP/IP settings are all correct and the log on the for the domain is correct, Now why am I not getting the prompt for the username and password. The machine is detected on the server because pinging to the server works but I can’t access all the network drives. Someone please help me get my prompt for username and password back. Thanks