Farmer, maybe, having unhappy experience with computer network (9)
I believe the answer is:
landowner
'farmer maybe' is the definition.
(a farmer owns land)
'unhappy experience with computer network' is the wordplay.
'unhappy experience' becomes 'downer' (a downer is a depressing experience).
'with' means one lot of letters go next to another.
'computer network' becomes 'LAN' (abbreviation for local-area network).
'downer' after 'lan' is 'LANDOWNER'.
'having' is the link.
(Other definitions for landowner that I've seen before include "One possessing estate" , "One with title to an area" , "One with estates" , "Squire, perhaps" , "One may have lots of grass" .)