Audio output problem

[agc77]

I had this problem once before but with bootcamp on my windows side, but now it's happened on my mac side. My audio has no output on my speakers, and it just doesn't work. When I click the Volume Up key, a little circle with a diagonal appears, meaning there is no sound. My headphone input has a red light coming out. When I input my headphones the sound works. When I reboot, the audio works perfectly, but as soon as the OS starts, it disappears. Can anyone help me?