I have a 91 honda accord that I have had for about 2 months. It was originally my brothers car and he sold it to me cheap because there was a problem with it. The car would run for about 8-10 minutes until the engine heated up and then I would lose power-everything. I brought it to my mechanic and he ran a diagnostic and replaced the distributor (for $350) but now after having the car fixed for about a month a new problem has come up. I leave for work at 8 in the morning car starts fine, but when I go to leave work at 4 in the afternoon it won't start. Sometimes putting it in neutral first helps but sometimes it doesn't. I don't see how my mechanic could have missed a problem with the relay when he was running a full diagnostic, is there anything else it could be.

Replace the main relay, which is located under the dash and to the left of the steering column (hidden by the silver cruise control box, which needs to be removed).

You likely got a steal. For a few bucks these cars can usually be made almost as reliable as new.

The only thing else it could be is a bad ignitor. If the mechanic installed an aftermarket distributor, this is a possibility. I would replace the main relay, first, and see if that solves the problem--I believe it will.