My tv's picture does not cover the entire size of the tv. The picture that shows is the size of a square and my television is a rectangular size. How do I widen the picture?

it could be you have pressed the old teletext service button, look for a button with 3 lines on it in a box and press it or try turning the tv off at the plug then back on again.

Assuming a modern TV with a square/rectangular arrangement of holes (i.e. VESA mount) - they're M4, length varies.
Appropriate screws will be in the kit with the wall bracket.

Check your cables connections and try other input plugs. If you are trying to watch a DVD, check your dvd (or other equipment resolution/size options. Nothing in the user guide gives you setting options. Although you should hit the PICTURE button and try different options.

I assume you have a wide screen tv? most TV show are broadcast in a square (4:3) format, on a wide screen television the screen is rectangular, so to fit the square picture on the rectangle screen you have to either crop the top and bottom, or stretch and distort the image. the only real solutions are either to watch everything in the 4:3 format (leaving the sides of your screen blank), or subscribe to HD which will broadcast most programs in a wide screen format with out distortion.

To adjust the picture size on the television itself you would need a Sharp remote because there is a view mode button on it but there may be another way. If you are connecting a cable box or satellite tv receiver box to this television that remote should have an hd zoom # button or format button or aspect button that would adjust the picture size. The tv would have to be in the right input and the cable box or satellite tv receiver box would have to be set to the proper resolution according to what this tv is supposed to be able to display.

If the physical size of your screen is 4:3 the only thing it can show is a compressed version. The screen is physically not able to show the true 16:9 version. The true 16:9 HD signal has been developed to show on a screen that is twice as wide as it is long or 16:9 ratio. Your screen is almost square or 4:3 ratio. I hope this helps. Thanks for using fixya.

Most likely it's the closed captioning has been turned on. From your post I assume you have the remote control and able to access the menus so try to turn off the closed captioning. I'll be notified if you post something new.

It turns out that the Closed Caption option was turned on somehow. When I turned that off the Black Square went a way and did not return.

change the aspect ratio

Check that you arent in close caption mode ( usally in the menu)