Reset? I wonder how I can reset the calculator without having to open and take the batteries out? Or how I can change the setting that does that the calculator round off by it self to 2 decimals?

Checking the batteries is the first thing one should try. It is possible that for some reason the screen may be too dim.
Reset the calculator by pressing the button on the back. The screen should show the menus. To adjust the contrast you must press the E key (no need to press the ALPHA key for that.) then press F1 to access the contrast setting feature. Press the Right pointing arrow to increase the contrast.

When you clear memory, the contrast sometimes changes. If the screen
is faded or blank, adjust the contrast by pressing 2nd and up- arrow or down- arrow keys .

Resetting RAM restores RAM system variables to factory settings and
deletes all nonsystem variables and all programs. Resetting defaults
restores all system variables to default settings without deleting variables and programs in RAM. Resetting RAM or resetting defaults does not
affect variables and applications in user data archive.
Tip: Before you reset all RAM memory, consider restoring sufficient available
memory by deleting only selected data.
To reset all RAM memory or RAM defaults on the TI-83 Plus, follow these
steps.
1. From the RAM ARCHIVE ALL menu, select 1:ALL RAM to display the
RESET RAM menu or 2:Defaults to display the RESET DEFAULTS menu.
2. If you are resetting RAM, read the message below the RESET RAM
menu.
• To cancel the reset and return to the home screen, press .
• To erase RAM memory or reset defaults, select 2:Reset.
Depending on your choice, the message RAM cleared or Defaults
set is displayed on the home screen.

Having gone over a month without a reply to my query, I assume the suggested contrast adjustment solved the problem.

Try to reset your calculator.
Press 2nd and then MEM it's right above the enter key on bottom right. Look for reset. Should fix your problem.

I'm not sure if it is the only solution, but I had the same problem and I replaced the batteries. My HP35S works fine now.

Previously, however, there was no "battery" annuciator on the screen. This calculator went four years without a bettery change. My HP48GII, on the other hand won't go two months without a change. Go figure.

Having gone over half a year without a response to my query, I assume my suggested reset solved the problem.

Having gone over four months without a response, I assume my suggestion to adjust the screen contrast solved the problem.

I had the same problem as this. This is because when you might have changed the contrast on your calculator when your old batteries were running low and you need to reset the contrast. Here is what you do:

press the orange "2nd" button, then press the "down arrow" button, then the orange "2nd" button, then the "down arrow". do not press the buttons at the same time only one after the other and KEEP GOING. The screen will eventually lighten up and you are all set.

I have read that to invert the LCD-screen you just flip the polarisation-plate (the plastic film that sits over the LCD display) 180º, that is, upside down.
Did you or someone opened your calculator? He might have reassembled it wrong. Or was it a prank?
If that was not the case, your best change is to reset the calculator and see if it solves your problem.
To manually reset your graphing calculator:

• Remove all AAA batteries.
• Remove the back up lithium battery.
• Leave the unit empty for 5 to 10 minutes.
• After the 5 to 10 minutes, place all the batteries back into the graphing calculator.

This process should restore the graphing calculator to the factory settings.

Good Luck!

Round to the nearest tenth.
6.36