The paper by Mark Haiman: Conjectures on the quotient ring by diagonal invariantsConjectures on the quotient ring by diagonal invariants J. Algebraic Combin. 3 (1994), no. 1, 17-76 starts with:
It has recently been discovered, mainly on the basis of evidence obtained using the computer algebra system MACAULAY, that there seem to be unexpected and profound connections between a certain natural ring and some fundamental and much-studied aspects of combinatorics and algebraic geometry.
Haiman's conjecture that he discovered by a computer was eventually proved by himself using (human) but deep algebraic geometry.