When disturbed, I can't — I have to be doing nothing (8)
I believe the answer is:
inactive
'doing nothing' is the definition.
(I've seen this before)
'when disturbed i can't i have' is the wordplay.
'when disturbed' is an anagram indicator (I've seen this in other clues).
'i have' becomes 'ive'.
'i'+'cant'='icant'
'icant' anagrammed gives 'inact'.
'inact'+'ive'='INACTIVE'
'to be' is the link.
(Other definitions for inactive that I've seen before include "Resting" , "Having no effect" , "Unoccupied" , "Not moving/working" , "Still" .)