Motherboard problem

I have just installed a new Gigabyte GA-81PE100 PRO2 MB together with 512 mb (2×256)+ P4 3.0gh + new 420 watt PSU + 80 gig seagate barracuda h/d.All booted OK, set Bios etc., still OK..started to install Windows XP OK, but halfway through install system closed down.Now will not boot at all. There is power to the MB. When the system is powered up the fans “TWITCH” once .If I remove the ATX 12V Power Connector all the fans spin OK.. IS the MB BAD ???? Any help would be very much appreciated. Thankyou. Tony…