Hi, My Descktop is optiplex 755

I try to change battery for clear CMOS but after put the battry again Dell power on and stay on 123 LED Message and two beep but monitor does not any sigal and said cable does not connectied...!!!

I use DVI cable and befor remove the battry everythink was working well just I can not setup nvidia quadro nvs290 driver. but now monitor does not work, also I can restart computer when I hold cltr+alt+del on keyboard

Please advise me to fix this issue 

Thankns in advance