You are describing a display that the baclight is no longer working properly. Unless the magnet was very heavy or very powerful, it likely did nothing and the problem is coincidental.
Is this system still under warranty? If so, return it for repair.
If not, you may simply need to swap the display yourself.
Does the system work properly with an external display?
Yes the system works fine with an external display. That was an option I was thinking of (Installing a new screen) and it looks like I will be doing that.