abit kd7a start up problem

Just built a new pc using an Abit kd7a board and amd 2200xp CPU, when
powered on there is no activity, no post, nothing apart from hard disk
spinning up. Hit reset button and it will then boot normally with no
error. Have removed all expansion boards Inc video card, with no
difference. BIOS upgraded from kt400a-8235-6a6ly-a1fc-11 to -13 but
no difference. Tried resetting bios settings. It doesn't to boot if
CPU speed is set to 1500. I have previously built two other identical
machines and one also has the same problem but the other is ok.
Problem is clearly not down to os as the machine doesn't even get as
far as post. Video card is msi mx440-t8x however removing this makes
no difference, and changing for a different non agp card also makes no
difference. Any suggestions?