If they lied about replacing the fan and did not do what they said they would, they commited fraud (if they intentionally lied) and/or breach of contract (not doing what they agreed yo do). If they damaged your keyboard through carelessness, they are liable for the negligent damage to your property. Based on what you write, you could sue them and potentially recover whatever you paid them for work they never did; for the cost to repair whatever damage they did; and possibly for a lost day of work, if a court agrees that it was sufficiently foreseeable that their actions would cost you a day of work. Note that because you are not a computer expert, you would need one who has examined your machine (such as the other technician you consulted) ti testify about the damage, about how the fan was not replaced, etc. You would presumably have to pay him for his time.