Did you only turn off the DHCP function of your router, or did you also change your network settings on each PC to have a static IP? Just making sure I didn't steer you off a cliff :)
DHCP is enabled. I went to the "Fixed mapping" tab on the DHCP page and copied my MAC address and IP address into the section labeled "ID #1". I then selected "save" and was prompted to reboot the router, which I did.