When your computer can't get an IP address, either the computer can't properly communicate with the router or the router's configuration has the DHCP server (the part of routers that gives out IP addresses) turned off.
It doesn't sound like you've changed anything, so maybe your router just had a bit of a hicup. Turn off both of your machines, unplug the router, and turn off your broadband modem. Wait a couple of minutes. Turn the modem back on and let it fully initialize (takes about thirty seconds). Turn on the router and let it initialize (takes about thirty seconds again). Then turn on your machines and see if that cleared up the problem.
If that didn't fix your issue, we are going to have to figure out what went wrong with your configuration and what caused the change.