Start a computer again (6)
I believe the answer is:
reboot
'start a computer again' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reboot that I've seen before include "Start notebook again" , "Recover from crash" , "Start up a computer's initial program again" , "Re-start up a computer's initial program" , "Start (computer) again" .)