Cisco 870 and Dhcp

hay,
I have a cisco 870 router at my house. It does not like to get a dhcp address on its wan interface over my cable internet connection, and charter says they can’t give me a static address as a home user. under the wan interface i have
ip address dhcp
this should work, and occasionaly it does. but if the house looses power, the router doesnt pick up a new address and i have to turn the interface off and ojn repetedly for anywhere from 30 min to an hour to get it to pick up an address. is their another command similar to ipconfig /release /renew i can use\/