Up mini print halfway

Hi

i have a up mini printer. the printer prints all fine but then it

  1. starts printing in the air
  2. or sometime stops generating the filament.

And additional question,

  1. can i shutdown my computer when the printing codes have been sent to the printer and its start printing?

  2. do i need to clean the head of the printer? and how to clean ? thank you

thank you. am newbie to 3d printer.