I'm located in Los Angeles with the parent company in Chicago (where we get paid out of). I signed an agreement when i started here approx. 2-1/2 years ago that overtime is paid as straight time. I am an full-time salaried employee who is non-exempt. I've come to realize or at least think that i've been short changed for approx $10,000 of overtime that should have been paided at time and a half. Do you feel that by me having signed something stating that i was to be paided at straight time override anything by the fair labor standards act??

No, generally speaking, you cannot sign away such legal rights. You appear to be within the time frame for filing a claim for unpaid overtime wages.
http://www.dir.ca.gov/dlse/HowToFileWageClaim.htm