Need help from computer wizzes! using another monitor

Sorry I don't really know where to put this discussion so the mods can move it to wherever is appropriate.

Here is my problem. I've been waiting for months to have the time to play BG2ee but now that the time is finally here (insert excited Boo squeak) my laptop decides to be a jerk and the screen keeps flashing from dark to bright, and is now really really dark. This has been an ongoing on/off electrical problem that I need to fix when I return home next month.

I was hoping to use my older laptop as a display to play the game on, yet I have tried and failed to do this. Keep in mind my computer intelligence is about that of a barbarian who has just fought an Illithid.

What I want to do is use my old laptop as a screen for my new laptop, which has BG2EE installed (i even installed mods for the short period my computer seemed "fixed"). I have a HDMI cable, but don't know how to set it up. I've tried putting it in both ends to connect the two computers, but when i try to extend display nothing happens. Can anyone help me? I'd be super appreciative

Thanks you everybody!