I have the same TV as yourself but have not had any of those problems that you mention, but i will give some suggestions to maybe cure them.
1. Make sure that 'Automatic Format' is turned off in the menu(press menu, right 5 times and its one of the options under heading 'Feature Menu'). This might cure the switching problem.
2. Have you adjusted the default contrast and brightness settings?(the default ones are far to bright (set to make pic look good in the shop)). Ideally you should have Contrast at 65 and Brightness at 45 (or as close as depending on amout of light in your room), also turn off Black Stretch mode.
3. Have you set-up your dvd player properly? Have you told it that you have a 16:9 (widescreen) TV?. This option should be in the set-up menu, i'm only guessing as i dont own one.
4. Code for Yamaha remote i can't help with. Have you thought about a learning remote? The best sensible priced one(under £100) would be the Cambridge M1
http://www.richersounds.co.uk/index....l.php&p=200839 its a doddle to use and set-up and will control just about anything.
Hope some of the above works, if it dosn't im sure someone else will have the answer.
Good Luck