need for speed most wanted keeps freezing up on xbox 360

I tried making a friends game then going public ONCE. The game froze during the transition. So I dont try that anymore. Also, I too run my game from the HDD. I have concours and I understand that is a big issue. I did all the SP first and when I logged into MP, my SL was almost 69. I was gaming with all foreigners so the concours problem I did not hear about. No one on my friends were on when I hit SL 71 so I passed Concours(mistake2). I am thinking that after this morning tradegy, buying this game was mistake 1).