Router weirdness... virus maybe?

My router is capable of acting as a DHCP server... and up until a couple of days ago... I used it that way... then all of a sudden one day, my wife got on the PC and she had no connection. I checked all of my pysical connections... my XBox and PS2 had internet access. From my browser... I tried to check my router settings (http://192.168.0.1). I couldn't even connect to my router from my PC. Then I checked my PC NIC Card settings for TCP/IP... Well... I have had them set for "Obtain an IP address automatically" (DHCP). Well... using IPCONFIG... I saw that my PC was assigned a VERY WEIRD IP address that was not even on my router's DHCP table. Also... it said, "Lease obtained: Jul 7, 2003. Lease expires: Jul 14, 2138" When I tried to release the IP address... my PC would freeze for about a minute, then I'd get an error. I am using Windows XP, BTW. But... just 5 minutes ago... I finally gained internet access to my PC... but I had to NOT use DHCP and I had to manually input my desired IP, my gateway (router IP), and my DNS. Now I have an internet connection to my PC... but... why is DHCP not working for my PC anymore? Are there viruses out there that screw with your network settings?