Desktop computer won't connect to monitor.

Hello,
My Desktop computer won't connect to my monitor. It is a Dell Optiplex 755. I had to replace the Hdmi cable because my bunny chewed in it and I thought that that would fix it but it didn't that's why I'm here now. When I plug in the computer and trun on the monitor a message pops onto the screen that says "There is no signal coming from your computer. Press any key on your keyboard or mouse to wake it up or press the input button on your display to switch to another source.". I have tried everything it says to do and nothing works. What can I do? Is there anything that I can do to fix it? Oh also, the computer just stays on even when I press the power button on it the only way to turn it off is to unplug it. Sorry for the long post but I'm trying to give as many details so hopefully someone can help me fix my computer.