mac pro wont boot after hd install

So here is the problem,

i have, 2008 MacPro, 2.8ghz 8 core, 12GB ram, stock 320HD. snowleo

i installed in slot 2 samsung 1.5tb HD. 5400rpm

after that nothing, no start up,

the fans power up, the ram lights come on and off the graphics card fan comes on.
there is power coming out of the usb's as the mouse lights up when plugged in but a keyboard will not work if connected. i get no chimes on start up.

i have checked both HD's externally and i can boot my macbook from the 320 fine.

reset smc didnt work, reset rtc didnt work. ( i think, the mac guy was bad on his instructions) removing the new drive didnt work.

what do i do next?
what is the button behind the ram for?