Hello I just bought a Sharp TV 42 inch LCD... it has a function to set a custom picture and sound mode called AV Mode. When I switch it to my preferred settings it always goes back to a Dynamic Fixed setting is there a way I can lock my customs settings on my TV?

The user manual for that TV can be found here:

http://www.sharpusa.com/files/tel_man_LC42D62U.pdf

Page 36 shows how to use the AV mode.

According to the manual, you can select a different AV mode for each input mode. That's what I would have expected.

Take a look at the manual and make sure you aren't doing something weird.