1. Directly connect your computer with modem and see if it works.

2. Is 'Send' signal in your router blinking? Try reseting router (unplug power plug to router, and then to modem, wait for one mins. .and connect back..). Check if it works.

3. Try  >> ping google.com    (in windows )

       OR  >>ping -c 3 google.com  (in LINUX)

  If packets are lost, call your ISP provider (easy ;-))

4. If it shows connected status, but no signal (or slow), - call your Internet Service Providers. Do you have broadband subscription with video? Most possibly it is the signal level issue. TWC has this issue so often.