Most likely you have not been able to release and renew the IP,and or diagnose/repair the connection.
1. Click the Start Button (the circular button with the multi-colored Microsoft symbol,then look for programs or all programs,then find Accessories,in accessories find "Command prompt" before opening it by clicking twice with the left mouse button,click on it once with the right mouse button and choose the "run as administrator" option,after this the command prompt will open.
2. At the cursor "the little blinking bar" type "netsh" (enter) - interface (enter)- tcp (enter)- reset(enter).
3. If successful the cursor will return to the next command line,after a few seconds it should return the the prompt if you see an error such as 'NETSHH' is not recognized as an internal or external command, operable program or batch file. Ensure you have typed the command correctly and that you have Windows Vista.
4. Restart the computer,if it is still not connecting then it,will most likely need to be escalated for further action according to your ISP's established procedure.