Oh dear! Nothing works (4)
I believe the answer is:
oops
'oh dear' is the definition.
(I've seen this before)
'nothing works' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'works' becomes 'ops' (I've seen this in other clues).
'o'+'ops'='OOPS'
(Other definitions for oops that I've seen before include "Silly me, I've dropped something!" , "My bad" , "statement after accident" , "Harem" , "Exclamation on making minor error" .)