My external screen is not detected by my lenovo windows 10 anymore

Hello,

my laptop just doesnt want to detect my external screen anymore, i used it just a few hours ago but it just doesnt detect it anymore. only thing happened was i disconnected the screen and by mistake chose pc screen only on the "project" menu and when i connected the screen again i tried changing it back to second screen only but it didnt work....any help??

Thanks in advance

also please tell me if i need to clarify something about the screen or the laptop im pretty much a newb so....:)