televisions and projectors

i have a rca 27 inch tv in my bedroom.  model # F27664.  up until now, it's worked just fine.  last week the picture was good, but the speakers didn't work.  i took the back off and blew out all the dust, put it back together, it worked fine until today.  i took the back off again, but, now i have to plug and unplug it from the wall to make the speakers work.  when i plug it in, it'll work about 7 seconds.  picture stays on, no volume.  can you help me?