MacBook 4,1 (Early 2008) slow and audio flickers unless headphones plugged in.

Recenttley my Macbook has developed an interesting issue. When my headphones are unplugged the speaker pops and the volume icon will bounce between grey and black. While I try to use the MacBook it freezes and becomes unreponsive, but if I plug my headphones in the volume icon remains black all the time and the speakers quit poping, and the computer quits freezing. Unplug them and instantly the laptop is freezing again.