Problem connecting to the internet

Greetings all,

I am an inexperienced Mac-user who use a Powerbook G3-500. It is running OS X 10.3. I use the computer for work and personal use. Two days ago, I upgraded the OS X to 10.3.5 via software updater, the file was 24 Mb in size. Everything was fine back then, I could browse the internet at work and at home. The problem started last night when I was browsing the internet at home. An hour into browsing the internet, it suddenly stopped. It wouldn't let me access the internet, it keeps saying Safari can't find the server. I thought it was the ISP problem, however, my windows computer can connect to the internet just fine. My connection is using a modem and a router. The PB is assigned an IP address by the router 192.168.0.4. I can ping the router and the windows computer.
I can't seem to find out what the problem really is. Any help would be greatly appreciated.
Thank you very much in advance.