How do I fix this desktop computer problem?

Question by CHT: How do I fix this desktop computer problem?
My parents turned off my computer by unplugging the power cord about a month ago while I was away. Now my computer desktop tower and my monitor are not syncing. I hooked up my laptop to the monitor and it worked okay, but now I am not sure how to hook up my tower to my laptop screen to check that. Any idea what may be the problem with my desktop, or for starters how to hook up my desktop tower to laptop screen?
The tower is plugged into the monitor, both are on, but the monitor shows a black screen when attached to the tower.

Best answer:

Answer by amvcross
if your pc has a non Integrated graphics card you may actually have two ports on the back of your cpu for a monitor to connect if so you have to use the port connected to the video card

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