firing switch help on xps 8300

i have a xps 8300 that i used for a month back in 2013 then it sat in storage and was well taken care of so its  pretty much new still other then i cant seem to figure out how to start it up after transfering the motherboard to a gaming frame. i hook up the wiring as stated on the motherboard but when i go to fire it up the fan spins for a second then then nothing. iv tried the take everything off and add piece by piece method and still same outcome.  if there is any way i can get help on this i would really appreciate it because id hate to have to waste a brand new computer.. thank you