I had a lot of issues finding a solution to my Nspire being stuck in a boot loop, all the boot loop solutions I found didn't work for me.
What worked for me and saved my nspire from the grave is as follows:
Remove the battery from Nspire
Ensure there is no power cable connected to the Nspire, then hold down [doc], [enter] and [EE] all at the same time.
While still holding down the buttons, plug your Nspire into your computer or a wall outlet. It should open into the maintenance menu.
In the maintenance menu, you will need to both format your file system and delete your OS. Once done with this, reboot your calculator. When it repowers, if it tells you to reinstall the OS, you're on the right path.
Visit this website https://nspireconnect.ti.com/nsc/ and connect your calculator. You may need to move the USB connection to different ports on your computer for your calculator to show up.
Once connected, click update OS, and install it to your calculator.
Hopefully, your calculator is fixed; this worked for mine.