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Step 4: Intensive care

Time to reinstall your OS.

1. Find a source for your OS. This can be a computer (via the official TI site) or another calculator with the same model. Just make sure you know how you're going to send the OS before continuing.
2. Take out a battery.
3. While still holding the battery in your hands, press and hold DEL. Hard.
4. Insert the battery while still holding down DEL. Your calculator should give you a message saying either Waiting... Please install calculator software now. (on a TI-83 Plus) or Waiting... Please install operating system now. (on a TI-84 Plus).
5. Without pressing anything else, install your OS. Be patient, as it may take a while.

Now try turning it on.

If it turns on

It was only your OS that got corrupted, and you've fixed it now. In fact, all the programs you had in archive should still be there! You're done!

If it still doesn't turn on

Go back to step 3 and try the "CLEAR + ON" boot again. If it still doesn't work, your flash chip (which holds your archive and OS) is corrupted. Unfortunately, the only way to fix it would be to clear it entirely, so everything will be gone. To fix your calculator, carefully do the following steps.

1. Find a source for your OS. This can be a computer (via the official TI site) or another calculator with the same model. Just make sure you know how you're going to send the OS before continuing.
2. Take out a battery.
3. While still holding the battery in your hands, press and hold DEL. Hard.
4. Insert the battery while still holding down DEL. Your calculator should give you a message saying either Waiting... Please install calculator software now. (on a TI-83 Plus) or Waiting... Please install operating system now. (on a TI-84 Plus).
5. Without pressing anything else, install your OS, but halfway through, pull a battery. Be strong; we know how tough it is to kill someone you love.
6. Your OS should be sufficiently corrupted now. Turn your calculator back on, and it should go straight to the Waiting... screen, no DEL trick needed. Press MODE.
7. It'll start "testing" your flash chip and display periods. This deletes everything on your flash chip, OS and all, so that your calculator can start completely over again. When the periods stop displaying, you can pull a battery, even if it's doing something else.
8. Turn your calculator back on. It'll go back to the Waiting... screen. Install your OS now, and let your calculator finish the installation in peace.

Your calculator should be as good as new now. You're done! Unfortunately there's no way to get anything back, but at least your calculator works!

If your calculator didn't even start testing your flash chip, your certificate's corrupted. (You don't have to know what this means; all you have to know is that something's really, really wrong with your calculator.) I'm sorry to tell you this, but your calculator's completely bricked. My best advice would be to just call TI and demand either a new calculator or a refund (assuming this didn't happen).