Read the following from the TI knowledge Base. Hope it helps
Reinstalling the OS fot the TI84Plus
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 the operating system on a calculator with low batteries. Users will need to use the TI Connectivity cable and the TI Connect to send the operating system to the calculator. Make sure to have the latest version of TI Connect
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.
If the message "Error! Press any key to turn unit off. Then turn unit back on." appears on the graphing calculator, quickly, remove one battery from the calculator and reinstall it while the transfer is taking place.