headphones are not working when plugged in

I bought a new ASUS laptop a few days ago and realised that the headphone jack may not be working properly. The headphones themselves work (I've checked on my ipod) but they're not being registered by the laptop when I plug them in and the sound keeps coming through the speakers. I've checked the device manager in the control panel but the only devices under audio are the laptop speakers. When I plug the headphones in, they're 3/4 of the way in, sticking out quite a bit and looking like they're not plugged in all the way. I've tried pushing them in further but I'm afraid to damage the jack. The headphones are 3.5mm, but I can't find the size of the jack anywhere to see if it's simply too small. Any advice?

Thank you!