Try checking at : right-click to desktop/Screen Resolution. Thats where i manage my setup (2 monitors 1 tv).
If this does not work i found that solution
turn off secondary display
go to display settings, there probably will be only one display left - your monitor, and it will be marked as 1
restart your pc
after logging back in go display settings, make sure settings are same as in step 2
connect your secondary display
source : https://social.technet.microsoft.com/Forums/en-US/f9e088f5-5449-4ae6-97a3-92a972d3e1c6/multiple-monitor-change-number?forum=w7itproui
Have not checked the solution myself but the problem as i understand lies at the numbers of each monitor, like a priority. If your tv is marked as 1, it has priority to become a main monitor rather than your monitor that is marked as 2.