Best Buy sold me a floor model with out informing me

Hi
I bought a PC from Best Buy, it turn to be a bad computer, which constantly give me problems, I contacted the manufacturer (Compaq), they Diagnose the problem to me as a failure due to CPU fan in which created a great deal of noise, and they instructed me to take it to back to the repair at Best Buy. That same day I got another problem when I tried to copy a CD and the computer failed to do so. I took it to the Best Buy store for service, after holding my computer for a long time they call me to pick it up, they told me it has no problems and they charged me 24 Dollars for inspection fee, when I tried to protest that and request to see the store manger, they call their security for me and threatened to force me out of the store. They humiliated me in front of my kids. I have been treated unjustly and I feel that I been treated with discrimination.
I am in chuck and do not know what to do , please help me.
Sincerely yours
Hiba Qalyuby
Research Associate
Civil and Environmental Engineering Department
Wayne State University
Detroit, MI 48202
313-577 3608