Television and Home Theater

All, I need some help, I have an RCA TV, Model: F35750ST and the sound has gone on it.  The Warranty is up on it and I don't want to get rid of it, does anyone know how I can fix this or where I can get information on how to fix it?  It's a pretty big size TV and don't want to get rid of it.  Anyone that can help me out I would greatly appreciate it.  Thank you, Shannon

I have a Daewoo DWF28 TV which is a great TV but
occasionally switches itself into engineer mode.
Yesterday my son tried all of the buttons while the TV
was in engineer mode and managed to press ZOOM
repeatedly which reduces the vertical size of the
picture each time it is pressed so now the picture is
only one third of the screen and none of the buttons
seem to restore the picture.
Does anyone know which buttons to press to
reset the picture size please
and how do I get into and out of engineer mode at will

My tv has a protective screen which causes too much glare from outside light. Can I remove this screen and if so how?  How easily damaged is the screen underneath? I previously had a 52" Zenith without the protective screen and it was in good condition when the tv quit.