possibly its an earthing fault.Try and build it outside the case and just attach the video card.If it works then its an earth fault between mobo and case.You should fit those tiny fibre washers between board and case mounts.If no joy then its either power supply or mobo or even duff ram.As stated here have you got the cmos jumper set wrong? check the manual.Lets us know how u get on.
Thanks for the suggestions. Spent most of the afternoon playing. Well, it's up and running after a fashion.
First problem a dead processor Athlon 2600 due, I'm told, to the clips on the heat sink not providing enough pressure between the heat sink and the chip. The heat sink compound was barely scratched by the processor. The two arrived in a plastic, sealed container and sold as a pair The processor was replaced with a 2400 for the time bieng.
Second problen a duff stick of 512M 400 MHz DDR. Played hell with installing XP as the RAM was unstable. Replaced with 256M 266 MHz from another machine for now.
Some of the drivers supplied with the mainboard are not XP compatable. This yet to solve, but am winning.