When my headphones are plugged in, it still plays sound out of my computer’s speakers just like I don’t have anything in the jack. What should I do? Is my headphone jack damaged?
What computer are you using, is it a notebook or a desktop, custom or complete?
Also the audio card/device would be helpful to know in order to determine where the problem is.
First of all you should look into the Windows audio settings and make sure that the Speakers are set as default playback device and the headphone is properly detected when plugged in and automatically deactivated when plugged out (status disconnected).
If you have a desktop system try using an audio jack at the back of the case (from the motherboard or dedicated sound card) as in some occasions a front panel jack from the case might not trigger the speakers to be deactivated.
1) right click on volume icon and choose Playback devices
2) right click on empty space and select Show Disabled Devices and Show Disconnected Devices if available.
3) Select Headphones and enable
1) plug your headphone
2) open search and click on settings
3) type fix , from the list choose Find and Fix audio problems