Motherboard problem

hi..i have a similar problem with my pc...i changed my motherboard some days ago but the new one doesnt seem to work well....when i open my pc although it is working normally it can not post or beggin BIOS and the monitor has no signal....but if i reset the motherboard the everything looks fine...if i close the pc i have to reset the motherboard again to power it on....i have all the other parts guaranteed checked...