If it's an older computer, the 3.5mm jack may not be wired for a mic. Carrying the extra mic signal requires an additional contact in the jack. However the plug is designed to be backward compatible so you will get audio even if the mic part doesn't work.
How to fix: get a seperate mic and plug into the mic jack... or look for a 3.5mm "4 contact" splitter.
If it's an older computer, the 3.5mm jack may not be wired for a mic. Carrying the extra mic signal requires an additional contact in the jack. However the plug is designed to be backward compatible so you will get audio even if the mic part doesn't work.
How to fix: get a seperate mic and plug into the mic jack... or look for a 3.5mm "4 contact" splitter.