Tried working when exhausted (5)
I believe the answer is:
tired
'exhausted' is the definition.
(exhausted can mean very tired)
'tried working' is the wordplay.
'working' indicates anagramming the letters.
'tried' with letters rearranged gives 'TIRED'.
'when' acts as a link.
(Other definitions for tired that I've seen before include "Weary or fed up" , "Done in" , "Beat" , "Exhausted" , "Sleepy" .)