My 1997 Prizm ran well until 1 1/2 months ago. One day during several weeks of wet weather, I was stopped at an intersection and the car stalled. It took several minutes of retrying and it finally started. I drove it home and put a can of dry gas into the fuel tank. It would no restart. A mechanic friend came by a few days later and banged on the fuel tank. The car started again. I drove it to his home shop. He replaced the fuel pump but the car would not stay running. He then changed the fuel pressure regulator. The car again would flood, start, run for a minute period and then stall. He told me that it keeps flooding but he is not sure why.
Has anyone got an answer for this problem?

The cause is ignition system failure, the effect is flooding. Check/replace the easy stuff first; e.g. spark plugs and ignition coil. If the problem persists, the Ignition Control Module (ICM) may be bad. Coils and ICMs are problematic components on vehicles of this generation. Heat causes them to break down over time--particularly the microchip inside ICMs.

Fuel pumps are extremely reliable on modern-day cars. 90%+ of "crank but won't start" situations are electrical-related, not fuel.