Ti 84 Silver Plus won't turn on

Does it turn on with a cursor, Have you tried a fresh set (all four) of batteries, Is there any corrosion/dirt on the battery contacts and the I/O port that you can see, Have you tried any resets?

Try reinstalling the OS, that might resolve the problem.

There is no such thing as a TI89 Plus Silver Edition.

If you mean the TI-89 or TI-89 Titanium, press diamond / (the diamond key below the 2ND key, then the divide key).

If you mean the TI-83 Plus Silver Edition or the TI-84 Plus Silver Edition, press MATH left-arrow 4 .

Press 2nd and then LOG.. This should help

If your little sister did as you say, then the logical way to handle the problem is to revert the process.

1. Press [2nd] button and release it.
2. Press and HOLD the UpArrow.
3. As you keep pressing, the top right of the screen will show a series a number, starting with 3 maybe, as you cannot see the 1 or 2, and the display will darken.
   
4. Maintain pressure on, till the display is to your liking.

the screen died

I have the same problem. TI Connect recognizes my calculator and shows my device info. But none of my key input will work.

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 work, add a comment to this post and we'll go from there.

Remove all four AAA batteries. Press and hold down the ON key for at least ten seconds. Replace the batteries and turn the calculator on.

ON, 2nd, [up] arrow to change the contrast. Works 99% of the time....