Your best bet is to have a look through the control panel for the router, is there an option in there for enabling a DHCP service?
This should allow the router to automatically renew the lease on your IP address which
should alleviate your problem.
Maybe.....
I'll have a look around and see if I can find any other information on your router that might help you.
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You might find something on this page that helps:
http://kbserver.netgear.com/products/MR814v2.asp