Can high def screen on a tablet be switched to normal screen

It looks like you are saying standard definition pictures do not cover the screen like HD pictures do. Standard def is formatted 4:3 and high def is 16:9. They are not the same so your high def screen is made to display the not as tall but wider high def picture. In order to fill the screen with the taller and not as wide 4:3 aspect ratio std def picture you must tell the TV to stretch the picture or otherwise fill the screen.The TV will have controls you can exercise for this purpose and you can set it up to always show std def in a particular manner. The alternative, if you want the standard Def picture to look true to form, is to view standard def in Letter Box form. It's appearance will then include black panels on the sides of the picture. So the problem is not with the TV but in accepting older format pictures playing on newer format displays (TVs.)

It looks like you are saying standard definition pictures do not cover the screen like HD pictures do. Standard def is formatted 4:3 and high def is 16:9. They are not the same so your high def screen is made to display the not as tall but wider high def picture. In order to fill the screen with the taller and not as wide 4:3 aspect ratio std def picture you must tell the TV to stretch the picture or otherwise fill the screen.The TV will have controls you can exercise for this purpose and you can set it up to always show std def in a particular manner. The alternative, if you want the standard Def picture to look true to form, is to view standard def in Letter Box form. It's appearance will then include black panels on the sides of the picture. So the problem is not with the TV but in accepting older format pictures playing on newer format displays (TVs.)

You most likely will see the crack during normal operation of watching the TV. Otherwise it doesn't hurt the TV. The screens if available will be expensive.

are you on a standard def or HD tvs? b/c if you have the xbox set on high def, then you try to plug it into the standard def then you won't get a picture, but you will get sound. If you don't have a high def tv then go to a friends or someone you know's and plug it in to see if you get a picture.

Make sure your using a cable box that is compatible with a high def tv, if your tuning a high def channel and your converter does not support high def, it will only play the sound, no vidio at all.

There are certain settings on the PS3 that has to be changed each time that you switch from High Def to AV. You have to plug both cords in and turn the PS3 on and view the screen with the High Def. You have to go to Settings --> Display Settings --> Video Output Settings
then follow the instructions.
Watch this video and it will help you switch from High Def to AV.
http://www.youtube.com/watch?v=TBqfeIpKm70&feature=related

This is because you are not receiving a high def signal or you are not using your high def inputs.

well then your tv is going out and you need a new tv

When in high def and on the PC the formate buttom on the remote is disabled. The formate will have to be done with the high def remote or through the PC. You will have to contact the high def and the PC provider to adjust the format.