Ender 3 pro with a 4.2.7 board

I've had my Ender Pro, ver 1.0.1 with Marlin abut 3 weeks. In that time it has worked flawlessly. Now all of a sudden the nozzle stays up too high when time to print. I have leveled the bed several times, clicked set home offsets, chose my file and hit print online USB. I'm using Ultimaker Cura 4.10. But I can tell when it prints those two lines on the left, it is too high. about 12mm. I have tried to download newer firmware with no luck. Costs too much $$$$ to buy a machine every month. I know your gonna say flash the thing. I have no idea what that means. Yes this my first venture into 3D. Any help will be appreciated.
Thanks ya'll