I changed the batteries and now it will not come on

Hello,
Here it is from the horse's mouth (TI Knowledge base)

For the TI-83 Plus Family, TI-84 Plus Family:


Caution: The resets described in these troubleshooting steps will cause a lossof applications, programs and data. If at all possible please create backup using TI Connect™ first.

1. Try a new set of AAA batteries.
2. Adjustthe contrast by pressing and releasing the [2nd] key followed bypressing and releasing the up arrow; repeat as necessary. To adjust orlighten the display, use the down arrow.
3. Remove one of theAAA batteries. Press and hold the [CLEAR] key. While holding [CLEAR],reinsert the AAA battery and then turn the calculator on. Thecalculator should display the message "RAM Cleared". Release the [CLEAR] key and then press it one more time to remove the message.
4. Removeone of the AAA batteries. Press and hold the [DEL] key. While holding[DEL], reinsert the AAA battery and then turn the calculator on. Thecalculator should display "Waiting...Please install calculator software now". Follow the instructions for the TI83 or TI 84 Plus family to reinstall the calculator operating system (see below.)
5. Removeall of the batteries including the round lithium battery for 5 minutes.After the 5 minute period, reinsert all of the batteries and turn thecalculator on. Adjust the contrast if necessary.

Reinstalling the OS for the TI83/TI84 Plus family

How do I correct the Error Waiting...Please Install Calculator SoftwareNow message on my TI-83 Plus family or TI-84 Plus family calculator?

If an operating system (OS) update fails or is interrupted, the calculator will be in an inoperable state with the message Waiting...Please install calculator software now.The most common cause of a transfer being interrupted is updating theoperating system on a calculator with low batteries. Users will need touse the TI Connectivity cable and the TI Connect software to send theoperating system to the calculator. Make sure to have the latestversion of TIConnect installed on the computer.
In order to install the software please follow these steps:
1. Connect the TI Connectivity cable between the computer and the calculator.
2. Click on Start >> Programs >> TI Tools >> TI Connect >> TI OSDownloader
3. Follow the on-screen directions to reinstall the calculator's OS.
Ifthe message "Error! Press any key to turn unit off. Then turn unit backon." appears on the graphing calculator, quickly, remove one batteryfrom the calculator and reinstall it while the transfer is taking place.

Hope it helps.