Why does my Mac Thunderbolt Port not register a connection? I tried 4 different items on the port and nothing registers.?

I left a macbook pro hooked up to my second monitor as usual. Came in the next morning tapped the keys and the second monitor would not light up. I can't figure it out. I thought the Kids may have bumped the wire but I couldnt get it to work so I thought the cable was shot. I tried another cable but it didn't work. So I thought the monitor was shot. It just says No Signal RGB.

I took the monitor to another location with the computer. I tried the monitor on another Mac with the same cable and it lit right up. When switching back and forth between that mac and mine it turned on and off like a light.

I restarted the Pram, I restarted the SMC. If we go to Preferences+Option, it doesnt detect displays. If we go to More Info/System report/Thunderbolt, It says No device Connected. I'm Convinced my Port is Broke. Buddy thinks it's a setting because all 4 monitors won't work on her mac either, but they work on that mac at other location.

It worked when I left work and didn't when I came back. I know no setting were touched because my computer is PW protected. ANY help is appreciated. Apple doesnt have much info on this.

Thanks