sometomes motherboards hold a bit of electrical charge and wont boot anything until it has been discharged, but it will put power to everything i have had this problem myself.
unplug the main power cable from the motherboard leave for a couple of mins then plug back in. sometimes the fans will give a quick spin releasing the charge(.so dont jump back )but make sure main power cable at the rear of computer is unplugged before you do this i dont want you to blow the mobo
it may be a long shot but hey when in trouble anythings worth a try
1 Thermaltake Tsunami Dream case Jeantech 400w psu 220gig sata H/Drives Abit AV8 Mobo Socket 939 AMD 4200+ x 2 @ 2.6 ghz 2048 ram. 256mb Nvidia geforce 6200.
2 Abit AV8 350w psu AMD64 <A firstname.lastname@example.orgGhz 512 ram geforce tornado 128mb.
3 Advent 7038 laptop AMD 2500+ 512ram ATI 320 graphics. wireless.