Why will 2006 Pontiac Grand Prix not start? Engine light and reduced engine power.

Hopefully your code clearing didn't clear the stored codes that could tell you what's wrong with the car. Have it scanned to see what the computer is telling you. Randomly replacing parts and hoping you'll accidentally fix the problem is expensive and rarely works.

My 07 grand prix isn't so grand, my reduced engine power light came on for about the 5th time. Each time the mechanic says it's fixed but NOT! Changed throttle body n accelerator, no fix..what to do??

Has your mechanic carefully gone through all the electrical connections in the wiring to make sure they are clean and tight and dry. Modern electrical systems are incredibly sensitive and on older cars those connections can make all the difference between something working and not. If he's not up to the task take it to a shop that specializes in auto electrical.