My computer wont display on my dell moniter. HELP!

My computer has a bad battery and its screen is broken to the point where you can't see anything on it. So I used my dell monitor with it and it worked fine. Now all of a sudden it won't display on the monitor anymore! I have tried pressing func and one of the f# buttons again and it won't work. When it did display though, it would take a minute then my computer screen would flicker and then the monitor would turn on. Now all it does is sit there forever and not display on the monitor and the light on the monitor stays yellow. HELP ME FIX THIS PLEASE!