This should tell you what the problem might be; assuming all the connections are correct. Good luck.
MOBO is Biostar Biostar P4M890-M7 PCI-E LGA 775 for intel socket 775
This MOBO. is brand new just out of the box.
1) Press power switch.
2) Power lights in case comes on: HD turns on, CD and DVD drives indicator light turns on then off, Floppy disk indicator light turns on then off, all case and CPU fans run OK.
3) Motherboard does not boot, no beep sound; LEDs are both off. Screen has no post.
4) Press "reset" switch. and all works; POST runs, computer boots and runs fine.
All loaded programs run well. I run the operation system with no problem.