Display is very dark. you can see the screen if you hold it in the light the right way.

screen back light on the other side is busted which need replacement.

How to Change the Brightness of the Display

To darken the display, press the yellow 2nd button and then press and hold down the Up-Arrow button located in the upper right section of the keypad. Release the Up-Arrow button when the display has reached the desired level of darkness.

To lighten the display, press the yellow 2nd button and then press and hold down the Down-Arrow button. Release the Down-Arrow button when the display has reached the desired level of lightness.

As you go through this process, a number will appear at the top right corner of the display. If this number is 7 or higher when your screen reaches the desired level of brightness, then your batteries are getting low and may need replacing soon. This number will be approximately 3 or 4 for new batteries.

It may be the internal backlight that is failing. When the display has failed but still has power, take a flashlight and hold it close to the screen, move the flashlight all around the screen and check if you can see anything. The display will be dark, but you should be able to make out the image that is there with the flashlight technique. If you can see an image on-screen, then your backlight has failed and you will need to replace the monitor. Weather or not you see an image is not a critical issue, but a tool to verify if the backlight is off or some other issue is causing the problem.
Note, it may be difficult to detect an image on the un-light display, for example if you have a dark image as your desktop background. So make sure to fully scan your display (top to bottom, and left to right covering the entire screen) with the flashlight technique in order to see any image on-screen.

It may be the internal backlight that is failing. You can take a flashlight and hold it close to the screen, move the flashlight all around the screen and check if you can see anything. The display will be dark, but you should be able to make out the image that is there with the flashlight technique. If you can see an image on-screen, then your backlight has failed and you will need to replace the monitor. Weather or not you see an image is not a critical issue, but a tool to verify if the backlight is off or some other issue is causing the problem.
Note, it may be difficult to detect an image on the un-light display, for example if you have a dark image as your desktop background. So make sure to fully scan your display (top to bottom, and left to right covering the entire screen) with the flashlight technique in order to see any image on-screen.

The most common problem in the TI calculators is not a real problem at all. When you replace batteries, the screen display may become too light and you cannot see that the calculator is already ON.
Increase the darkness of the display. Here is how to do it.

1. Press the [2nd] key and release it.
2. Press the UP navigational arrow and HOLD the pressure.
   

On the Top right corner of the screen a number is displayed (between 0 and 9). The value changes as the screen contrast changes.
When the contrast is adequate (to your liking) release the Up arrow.

The most frequent cause for this ''not turning on'' is a screen that is too light to see anything displayed. Try increasing the screen darkness.
Press 2nd key and release it
Press and hold the Up Arrow until it is dark enough.

If the does not work

1. Press 2nd key and relese it
   
2. Press UpArrow and release it
   
3. Repeat the two steps until screen is dark enough.
   

Hi,
Check that the terminals in the battery compartment are clean and shiny. Remove any powder left after battery leakage. Insert fresh batteries in calculator. Make sure you respect the polarity diagram. +-+- (Many malfunctions come from incorrectly placed batteries).

After replacing batteries, calculator is restored to defaults and screen display may be too loght or too dark

To adjust the screen: Darken or lighten display

To darken screen
Press [2nd] key and release it.
Press and hold [UpArrow] until screen is dark enough.

To lighten screen
Press [2nd] key and release it.
Press and hold [DownArrow] until screen is light enough.

Hope it helps.

The Back-light on your LCD screen is bad, your crystals aren't illuminating, so it is dark.... very dark.

You need a new LCD screen.

Sorry.

Above the upper right corner, there is a littlesquare nutch that turns the screen dark when the lid is closed. In most cases it's stucked. poke it with a pen and see if the light turns on.

http://www.fixya.com/support/t675917-toshiba_m55_s135_screen