Macpro dont start up after restart

Hi, i buy a macpro 1.1 and today i install i few programs, after the install the mac tell me to restart and i acept that. the mac shut down and after that i hear a short sound ( maybe the disc???), the monitor is black, without any signal and the mac loops there with the sound..i wail a while and so i must shut down with the power bottom. the problem every time i have to restart the mac.

pls help!!!