Lose Router Connection

Using cable internet, all connections to the router/modem are lost. It's a combined router and modem, a Netgear Gateway CG814WG and when the event happens wireless and wired devices are no longer connected to the network. It usually fixes itself soon after. The event log shows the following every time it happens;
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) DHCP FAILED - Discover sent, no offer received
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Init RANGING Critical Ranging Request Retries exhausted
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Init RANGING Critical Ranging Request Retries exhausted
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) Init RANGING Critical Ranging Request Retries exhausted
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Init RANGING Critical Ranging Request Retries exhausted
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Time Not Established Critical (3) DHCP WARNING - Non-critical field invalid in response.
Time Not Established Critical (3) Init RANGING Critical Ranging Request Retries exhausted
Time Not Established Critical (3) No Ranging Response received - T3 time-out

This never happens if I'm simply using a computer, it fails when I'm using an Xbox 360 - but only certain games. If its relevant at all, the ports I've forwarded are 53, 80, 88, 2074 and 3074. Which I believe are all I need for it. I get the connection sometimes, and sometimes it works for an extended amount of time, but other times it will only connect briefly.
I've tried everything I can think of and scoured websites but haven't achieved anything. I'm relatively new to networking so I've very likely done someting wrong.