Posted 18 April 2010 - 11:02 PM
The first thing to check is to log into your router while the signal is "out" and see if it shows a connection, and a valid IP address, on the WAN port. If the address starts with 169.254.x.x and yet the port shows connected your lease has expired. The "Internet" light on the front of the router may go yellow (on some routers) when it loses the lease.
Some of the equipment used by cable companies is notoriously bad at handling DHCP requests, and if your lease times out your connection is kaput. The router will try to renew it's lease when it's half way through it's duration, so if it loses it entirely you can bet it's been trying for a while without success. Netgear and some other "house brand" routers seem to have particular difficulty getting a valid lease, at least from our cable company locally (Charter). I've done in-depth troubleshooting and presented them with a full write-up with traces and analysis of the issue (it's what I do, professionally, but this was for a friend who is also my bookkeeper and couldn't maintain a connection long enough to pay my bills). As far as I can tell they just trashed the document, and we ended up getting another router (we tried three before one worked) to make it work.
If this isn't it, look at the upstream router (Gateway) address on your router while it's working. Then try to ping or traceroute it when it is not working. That will tell you if the fault is local or wider based. Let us know what you find.