Macbook Air - Not possible to shut down, no sound, no trash, etc.

Hello,

Im experiencing a huge problem with my MacBook Air, version 10.6.8. It was in service 6 month ago, but it didnt help much. The points that are causing problems are the following:

- In the first place, if I want to shut down i click on the apple, shut down or restart and its starts to load but nothing else happens. It doenst shut down, it just loads, with the ball thingy.

- Same problem with the trash. I had to download TrashIt to delete some files, because when clicking on "empty trash", its starts to load but then it freezes and i have to force quit.

- Also, sometimes the bar (with the apple, clock, wifi, battery, etc.) just freezes, the rest works. I can browse the internet, write an email, etc. but when the cursor hits the bar i see the load ball.

-Finally, the sound. When clicking on louder for example, it pops up like normaly but i see like the sound volumen and underneath a circle with a diagonal. In preferences, no audio input nor output. Also, in - About this Mac, More Info - this appears:

Intel High Definition Audio:

Audio ID: 0

Maybe its relevant or not, but when watching a video, for example youtube (doesnt matter if Google Crome, Safari or Firefox) it stops to load every 5-8 sec. even if ts completly loaded.

I have no idea what to do... I hope you can help me!

Thanks.