I plug my headphone into computer's sound card. The headphone only
works when it is pulled out slightly. If it is fully inserted, some
sound won't play as loud as it should be (human voice is noticeably
weaker).

My speakers, and other headphone work well on the sound card.

Is this a compatibility problem, or my headphone is broken?

Headphone:
Cosonic Digital Stereo Dynamic Headphones (MDR-CD850) with volume
control
http://www.headphone.com.cn/sort1.asp?sort_id=95&page=2
Impedence: 32 Ohm

Thanks.