Replaced Motherboard in my Toshiba Satellite.....

I replaced the motherboard in my Toshiba Satellite M45, actually i got a near complete bottom,( of my exact model) that came with everything but the RAM, MODEM, HD,Wireless Card! So i put the parts from my old bottom, into it, and attached my LCD, and inverter cables. And when i plugged in the power adapter, i even got the power light to come on! so i went to turn it on, and it starts to power up, but suddenly shuts back off, and keeps doing this until i remove the battery! ive switched out the memory, HD, and battery even. and unplugged the lcd cable from the board, and plugged it in to the external vga, but still nothing! can anyone think of what else it may be, cause im about out of ideas!! thanks a bunch.......J