Mic on Ipod Touch 4G is turned off?

I just got a Ipod touch 4g yesterday. my mic is not working properly.

when i have no headphones plugged in the mic is turned off? if i plug headphones in, then the mic turns on. i can't find any mic setting on the ipod.

My best friend has a Ipod Touch 4G and his mic works both with and without headphones plugged in. why is mine not working properly?

i tryed restoring it twice and it still doesn't work properly?