You don't give enough information to describe the letterbox problem. If by letterbox, you mean that you might still have some black bars on the top and bottom of your screen, but the image fills your TV screen left-right, this may be normal. You need to understand that your 16:9 TV matches HD video perfectly, but when it comes to theatrical films, unfortunately films were shot in a variety of aspect ratios that just don't perfectly match your TV's aspect ratio. For example, there are films that were shot using aspect ratios of 1.85:1, 2.35:1, 2.40:1 and many others. These aspect ratios don't perfectly match the aspect ratio of your TV, so you will still see some bars on the top and bottom of your display when watching movies shot in these formats. This applies to both Blu-Ray and standard-def movies. If you just can't put up with the black bars caused by these formatted movies, you can simply use your TV's remote control and use the Zoom button to expand your TV's display. This will get rid of the black bars but the trade-off is that you've expanded the TV image causing a slight softness.
If by chance, your black bars are seen both on the top-bottom AND left-right, then you don't have the settings on either your DVD player or TV set correctly, and you need to read the manual on each to learn how to setup each for widescreen movies.
how to get rid of the letter box when watching blue ray disc. I have samsung bd-1600 and panasonic TH-50PX60U