Headphones not recognized

Hi, my computer doesn't recognize my headphones. The speakers work fine, the headphones work on other devices. They used to work on this pc too, but a few hours ago my friends and I were trying to record something with a mixing table and they had to change a few things for it to work. I have no idea what they changed and I don't know what to try to fix it... where should I start?

Try the System Restore and restore the PC back to an available restore date that is BEFORE whatever was done.

System Restore will not delete any user data or e-mails.

System Restore can be accessed from Start/Programs/Accessories/System Tools.