how do I get my external monitor to work with my Laptop

I had a toshiba satellite M115 with a cracked screen. I can see nothing but light through the crackks in the screen. I am trying to connect an Acer V173 as an external monitor and the monitor keeps saying”no signal”. I.ve tried the FN keys and nothing is happening. I have tested the monitor with anoth computer and it works with no issues. Help Please?!?!?!