Sticky stuff starts to get under new keyboard (4)
I believe the answer is:
gunk
'sticky stuff' is the definition.
(I've seen this in another clue)
'starts to get under new keyboard' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'get under new keyboard' is 'GUNK'.
(Other definitions for gunk that I've seen before include "sludgy stuff" , "Unpleasantly messy substance (informal)" , "Slimy, oily or dirty substance" , "Thick, sticky substance" , "Unpleasant sticky stuff" .)