Broken is the past participle of the verb break.
He has broken a window with a ball.
Broken is also an adjective. A broken object has split into pieces or has cracked, for example because it has been hit or dropped.
He sweeps away the broken glass under the window.
...a long table covered in broken crockery.
He glanced at the broken lock he was still holding in his free hand.
If a machine or device is not functioning because there is something wrong with it, you do not usually say that it ‘is broken’. You say that it does not work or is not working.
One of the lamps didn't work.
Chris sits beside him with sweaters on because the heater doesn't work.
The traffic lights weren't working properly.