Get lost with PC's routine using computers (4,2)
I believe the answer is:
beat it
'get lost' is the definition.
(both can be used to tell someone to go away)
'with pc's routine using computers' is the wordplay.
'with' means one lot of letters go next to another.
'pc's routine' becomes 'beat' (as in a police officer on the beat).
'using computers' becomes 'IT' (information technology).
'beat' put next to 'it' is 'BEAT IT'.
(Other definitions for beat it that I've seen before include "Clear off!" , "Scram, get lost" , "Get going" , "fly away" , "try out drum kit?" .)