Necesita una nueva batería de calculadora.

You need a new battery. Some people had success manually charging the battery but this is extremely dangerous and will cause a Lithium fire or explosion if you don't know what you're doing. If your battery is bulging at all then dispose it immediately and do not attempt any further charging.

This sounds like some sort of driver issue to me. Try using a different computer. You can also try using tilp which is an open source TI-Connect CE alternative. http://lpg.ticalc.org/prj_tilp/ (website is outdated but the download should still work for you)

It's common for a C to appear. Unfortunately I don't understand why it appears. What do you mean by 'it goes back to normal'? Is the calculator going back to the home screen?

This has become a problem with recent calculators. The problem seems to be the calculator can't charge a low battery anymore. You can contact TI Cares and tell them that your calculator boot loops and won't charge your battery. From what I've heard, TI has been pretty good about shipping people new batteries.

If they won't give you a new battery, you can try charging your battery in a friend's calculator.

Does your calculator boot at all? Do you have the Nspire CX or the Nspire CX II? The steps are different for each. The software should recognize the calculator even with no OS.

Does your computer recognize when the calculator is plugged in (does it make the 'new device detected' sound)?

Intente cargar la calculadora durante la noche durante al menos 8 horas.

Try charging the calculator overnight for at least 8 hours.

Unfortunately you can't buy units. You have to salvage screens from other calculators.

Look inside the USB port and see if there's the black plastic piece holding the gold pins in place. If it's not there, use your warranty to get a new one. In the meantime, you can switch batteries with a friend's calculator and let them charge yours.

You can also try a different power source and different cable. If neither works, then you'll need a new calculator.

The lack of a shield makes me suspect it has been disassembled before. Could you please tell me the date code on the back of the calculator? It will look something like L-0519M. This will help me identify whether it's a problematic model or not. You could try a new battery, but if it's a problematic model that may not work.