Pad set up; new beginning (4)
I believe the answer is:
dawn
'beginning' is the definition.
(I know that dawn is a type of start)
'pad set up new' is the wordplay.
'pad' becomes 'wad' (both can mean to stuff or fill).
'set up' is a reversal indicator (in a down clue, letters go up).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'wad' backwards is 'daw'.
'daw'+'n'='DAWN'
(Other definitions for dawn that I've seen before include "Aurora was its goddess" , "Cockcrow" , "Aurora, poetically" , "Break of day" , "Sunrise" .)