When computer's overwhelming Everyman's a kind of jelly (5)
I believe the answer is:
aspic
'a kind of jelly' is the definition.
(I know that aspic is a type of aspic)
'when computer's overwhelming everyman's' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'computer' becomes 'PC' (personal computer).
'overwhelming' is an insertion indicator.
'everyman' becomes 'i' (where 'Everyman' is the setter of the crossword).
'pc' enclosing 'i' is 'pic'.
'as'+'pic'='ASPIC'
(Other definitions for aspic that I've seen before include "Clear savoury jelly" , "Savoury jelly for meat or vegetable" , "Edible jelly" , "Savoury jelly used to coat eggs etc" , "Clear meat or fish jelly" .)