Dell 570 Inspiron / Unable To Contact DHCP Server

I have a Dell 570 Inspiron desktop running win7 home premium w/ a 64 bit OS. I have Frontier dsl with a Westell 327W modem and a netgear router. Two desktops are connected to the internet...one through the modem and the Dell 570 through the router. I also run laptops through the router w/no problem. This morning the dsl went down, and when it came back up, the Dell 570 would not connect. i tried Diagnosing Connection Problems, and I'm told to turn off the modem/router (which I have done a gazillion times).When I look at Network Connections in the Control Panel, It tells me I have an unidentified network and can't connect. I read through some forums earlier, and found that releasing and renewing ipconfig often corrects the problem, and that's when I got the message that 'An error occurred while nenewing. Local Area Connection unable to contact DHCP server.' This set up has worked for the past year and a half. I looked at the network adapter, and it says it's working properly. I changed the cables going to the machines, and they both work on this computer. The only change made to the computer was to install McAfee security center through AOL yesterday, but the set up worked all yesterday and last night.