Nothing in computer network is an advanced item (4)
I believe the answer is:
loan
'an advanced item' is the definition.
(money given as an advance)
'nothing in computer network' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' indicates putting letters inside.
'computer network' becomes 'LAN' (abbreviation for local-area network).
'o' going into 'lan' is 'LOAN'.
'is' is the link.
(Other definitions for loan that I've seen before include "Advance (money)" , "One acquired temporarily" , "Advance, borrowing" , "Something borrowed" , "Cash advance" .)