How long have you left it in that "shutting down" condition?
You don't mention what type of computer it is (laptop, desktop, tablet, 2 in 1, etc) nor the manufacturer name, model name, model number.
It's possible that it is having trouble shutting down a running process or it may be trying to complete an update or other process before shutting down.
Worse case.... if it remains unresponsive over a very long period then you could deprive it of its' energy source..... unplug it from the wall, remove the battery but only as a last resort.