1994 Pontiac Sunbird 3.1L

I have a 1994 POntiac Sunbird 3.1L. I have two problems with it.

1- One week ago, the car stop to work. The problem is that the car start to run some minites and then the motor stop. One friend to me that this is a problem with the computer. What your opinion.

2- The other problem is that the car blow out the coolant and the motor temperature become high. I performed and inspeccion and not leaks is observed.