ubuntu linux sound wont work

I installed ubuntu linux on my pc, but sound wont work. How do i fix it?

What you need to do is get acquainted with the Ubuntu help forums. There are lots of postings there from people who have had different problems. Sometimes sound, sometimes other things. Those forums will tell you what "GStreamer plugins not found means", and how to fix it.

Does the sound work if you boot from a liveCD? If so then it might be quicker/less painful to reinstall - that is not a major investment following a so-so install experience.

You don't say what your soundcard is, you don't say what your computer is. Go to the Ubuntu forums - they give you hardware specific fixit information.