Does the Trezor show “Trezor Bootloader 1.x.y” or “Welcome! Please visit [trezor.io/start](https://trezor.io/start)”?
In the first case, maybe the left button is stuck? The bootloader is entered if the left button is pressed while connecting the USB cable (Trezor One). Trezor T is similar, but it enters the bootloader when some finger motion on the touch screen is detected.
In the second case, it looks like the firmware was damaged. You need to install the firmware again. There is also a good chance that the Trezor is wiped afterwards and you have to recover using your seed phrase. Follow the recovery process and remember to only enter the seed words if your TREZOR hardware device asks for it (don’t trust what the website says). For Trezor One you can use advanced recovery to avoid entering the seed words in clear on the PC.