2004 Chevy Impala 3.4 not starting

ok jus wanted some opinions on what it can be...well it started about a month ago...and replaced the starter off the bat jus assuming that it was that since all the interior lights came on but no start...after replacing the starter it would only start when the brake was pressed...that only worked for about a day...then after that I read up and saw that I could cut the yellow wire to bypass that passlock crap and it would work...well that worked for acouple of days then it would no longer start...so we jus thought it would be the ignition cylender...so i replaced that and it started right up no problems then when we was putting the pieces back together it would only start every so often...so then my friend that works at a dealership took it in and ran tests and all test saying that it was the bcu...so i got a bcu and he replaced it and programmed it...and it started for the day and took it home and in a few hours it no longer starts...every once in awhile it will...so anybody have any idea on what it can be???

Does it crank but not start? oes the security lite stay on?

it dont crank...the security light comes on every once in awhile...its makin me angry bah...haha...but the check engine light comes on...

nvm...found out that i needed to replace the ignition switch and now it starts and runs great...blah