Firstly, determine that you have a good connection to your ISP, by going to Start-Run, then typing 'winipcfg' and hit Enter. You should have a bunch of numbers in the IP Address section. If they are all zero's, then your problem is with the dial-up.
Next we need to check that you have a good connection past your ISP. Go to Start-Run, but this time type 'command' and hit Enter. Within the black window type 'ping 192.148.252.54' and hit Enter. This will "ping" a DNS server to check for a good internet connection. If this returns a 'Request Timeout' or 'Destination Host Unreachable', then your ISP is having problems with their connection to the internet which should be temporary. If it returns the ping correctly, then your connection to the internet is good.
This then means that it is your browser at fault or your destination website is unavailable. Try running the connection wizard for the browser again, or confirm that it is the browser at fault by installing another browser such as Netscape. If Netscape also has problems, then the chances are that the destination site is unavailable at that time.
Hope this helps.