MacBook pro stuck in a loop after booting yesterday i turned off my computer as usual nothing strange yet ive noticed that it get so hot lately ( I figured out later that it’s due to dirt in fan , i cleaned it ) ; then today morning computer stucked in a black loop after apple logo , it shows in a half second cursor then it turn. Black again , i tried safe mode ( stucked in same loop )and repairing disk and reinstalling macos i tried alt command R+P and nothing worked , i didnt install anything yesterday yet i ignored an update from apple from last week ; im using sierra , i need help please , and thank you so much in advance
It sounds like the OS might corrupt hence failing to boot, you can verify this by booting up using verbose mode to see where it gets stuck at. 

To fix the actual issue I think you should boot into recovery mode and do a re-install of the OS (formally called Archive install) 
This shouldn't delete any data but if you had a backup then good. Here are instructions

https://support.apple.com/en-gb/HT204904