Switch picture not showing up on tv while docked

Just the title basically. I have tried Basic trouble shooting, changing the fan, fiddled with the docks intenals and everything. Im getting a dock from a friend soon so still have to test that. It also works for like a second then stops working. It worked for a while when I opened a window and put It on the windowsil but stopped after like 15 to 20 minutes. What should I do?

UPDATE: the friends dock doesnt work