Abandon computer studies completely? I don't believe you (5,2,3)
I believe the answer is:
leave it out
'i don't believe you' is the definition.
('leave it out' means you don't believe something)
'abandon computer studies completely?' is the wordplay.
I cannot really understand how this works, but
'abandon' could be 'leave' (to abandon something is to leave it behind) and 'leave' is found within the answer.
'computer studies' could be 'it' (Information Technology) and 'it' is found in the answer.
The remaining letters 'out' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
(Another definition for leave it out that I've seen is " Stop it!; Don't mess about! (inf)".)