That is frustrating, and it is worth working through these three checks in order before anything else.
Restore the firmware. Connect the device to your computer, go to code.circuitmess.com and click Restore firmware.
Check the solder joints. Look for cold joints, which are dull and lumpy, and for bridges, where solder connects two pins. Reheat any joint that looks doubtful.
Check the battery. Make sure it is charged and properly connected.
If none of that helps, message us here, or email [email protected], with photos of your circuit board, front and back with the casings removed, and a description of the problem, including what the device does when you switch it on.
Your device may have its own article, which is usually the faster route: Bit 2.0 · ByteBoi 2.0 / Wheelson 2.0 · Chatter 2.0 · Clockstar 2.0 · Codee 2.0 · Jay-D 2.0 · Synthia 2.0 · Rimac Nevera · Mars Rover · Artemis Watch 2.0 · Beep Boop