Google like this: Windows (insert version here) SAFE MODE.
Get to safe mode and set it to that or something close. Test.
Then reboot and see if it works. You are very light on details such as how this happened and what PC this is.
I don’t know what to do, my Dell monitor is saying that, “The current input timing is not supported by the monitor display. Please change your input timing to 1920*1080,60Hz or any other monitor listed timing as per the monitor specifications.” After seeing this, I attempted to change the display settings but I can’t get off of the black screen that says that now.