|Is your modem just a modem, or is it a "combination" unit that is also a router and a wireless access point?|
If it's a "combination" unit, are you connecting wirelessly?
If it's not a combination unit, call your internet provider. You'll need to replace your modem and they're the people who can help you do that.
If it is a combo unit and you're connecting wirelessly, click on my name above in my repsonse and read my "how-to" guide titled, "Troubleshooting Wireless Issues"
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.