1. Try other headphones. Unlikely to help, but you never now.
2. If the audio of this PC is bad for all headphones, it's a warranty issue. Back to the shop to have it fixed.
Microphones, by the way, don't give sound. They record sound.
i've had my current pair of headphones for about a year and they've worked fine but i am using them on a new pc now and the audio that comes out of the headphones are very low quality and the system sounds from the computer are also for some reason played through the microphone so if i'm watching a youtube video in a skype call or something everyone would be able to hear it playing from my microphone, i've tried about 1000 solutions the past 4 hours and i'm about to just call it a problem with the headphones its self (even though it's definitely not) if i can't figure it out soon, any ideas?