Dell Dimension 9150 freeze on POST with constant beep
 

My Dell Dimension 9150 worked well yesterday but today when I turn it on it freeze during the POST, the status bar under the Dell logo on screen go up to 95% more or less, emit a constant beep and the Diagnotic Lights 1 and 4 light up. I unplugged the keyboard, mouse, HD, DVD, monitor and video...