comuter powers up for 1 sec then restarts over and over again

my computer powers up for 1 sec then shuts off its using a intel dg41cn mother board i diconnected and removed all hdwr except cpu and it will run steady and post a 3 beep bio i then installed the grafix card agian a 3 beep bio. so i placed one card of ram in and again it shuts down 1 sec after powering on