Step 1

Check your cable modem is working.

Different modems have different light patterns, but normally there are a number of green lights displayed and at least one flashes regularly when the connection is working.

It is a good idea to get to know what light patterns to expect when the unit is working properly.

If only one light is on or there is a flashing orange light it is likely that the modem is down.

Phone your cable company to find out if there are any outages in your area.
(It may be worth reporting to your cable company that the cable appears to be down)

If the cable company is not reporting any outages, proceed to Step 2 to restart the modem.

Restart the modem.

Remove the power supply from the modem (this will be one of the cables in the back of the box, locate which cable leads to your mains plug and remove it from the modem). 
The lights will go out. 
Wait one minute and plug it back in again.

Wait one further minute for the modem to restart.

Check which lights are now on.
If only the power light is showing it looks like your cable connection is down. 
If one of the lights is flashing orange then your connection may be poor
If all lights are on then your connection is probably good.

If necessary re-check your internet connection once more as described in
FAQ 6 - How do I check that my internet connection is working?

FAQ 9 - to check How do I test my Link Sys Cable/DSL Router is working?

FAQ 10 - to check How do I test my Hub is working?