You might have to much shit plugged in. How many pcs \ consoles do you have going \ wireless devices? iPhones, iPad etc.
I stick with D-Link modems \ routers just because of previous experiences with them, I have had no issues.
How far away are you from your telephone exchange? ( Google, you will have to enter your address and stuff )
So you had internet working fine before? What happened since then?
Get a new modem perhaps, a ADSL2+ D-LINK Modem\Router all in 1 wonder is only like $110 roughly, you can always take it back if it fixes nothing.
I also had similar issues once where my Telephone cable was sort of kinked, internet was shitting itself, perhaps check and replace it.
If all else fails, unplug everything bar 1 pc or xbox, see if that helps, you might be overloading it. Probably not though.
Posted on Wednesday, 4th January 2012