Replaced all batteries, pressed on, pressed the 2nd key, nothing happens still

It is possible that the calculator went dead because the main batteries were depleted. However when you change the main batteries, it is often the case that the display contrast changes, and may become too light for you to see anything. If that is the case, you can increase the contrast of the screen.
Press the [2nd] key and release it.
Press and HOLD the [UpArrow].
The contrast should increase and the screen darkens. Keep pressing the UpArrow until the display is satisfactory to you.

It is possible that the screen dimmed too much after you changed batteries. One of the two procedures will work.

Press the [2nd] key and release it.
Press the UpArrow and keep it held down for a while. As you hold pressure on UpArrow key the screen should darken. Stop when satisfied.

Alternative.

Press [2nd] key and hold pressure.
Press the UpArrow repeatedly until screen darkens to your liking.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible. Does it?

Before repairing it, try this.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

If that doesn't do it, please reply to this post and we'll go on from there.

IT WORKED!!!! The manual on my 99 ML430 to "Resynching Remote Key" was just written weird.

It says "Turn the key in the ignition to 2nd position then back to 0. Press and hold the lock key for 15 seconds... now press the unlock key 5 times"... which I held down the lock button for 15 seconds, released it, then pressed the unlock key 5 times. NOTHING!

The newer manuals say press and hold the lock key and press the unlock key 5 times (with the lock key still held down).

So... it worked. Hope this helps!

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

If this doesn't do it, please reply to this post and we'll go on from there.

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).

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.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on at all. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

Batteries:
Make sure to replace the "battery backup" too the little lithium ion battery

Try Adjusting contrast:
Hold down "[2nd]" key press up or down arrow repeatedly to lighten or darken contrast.

First attempt reseting:
Step 1: Remove all the batteries
Step 2: Hold "Clear" key down
Step 3: Still holding "Clear" key reinstall batteries
Step 4: Still holding "Clear" key press "On" key until home screen is displayed.

Second shot reseting:
remove all batteries including lithium ion (backup battery), wait 3 hours and reinstall batteries.

Third Shot reseting:
Step 1: Remove a battery
Step 2: Hold down "DEL" key reinstall battery
Step 3: Possible msg pops up saying "Waiting ... Please install software" IGNORE msg and take out battery again
Step 4: Reinstall battery do not hold down "DEL" key

reseting will cause the handheld to loose all of its stored memory.

Hope that helps!

Try adjusting the brightness by pressing 2nd key or witchever name is on yours for the Alt key + the up or down arow key(as you see fitted)