after 2 days of playing with out problems...this started happening to me....
apparently i had too many save game slots used and when i deleted them it worked.....i dont know why...but if you are freezing at start screen..try deleting all but your most recent save game....it worked for me
update: nevermind...it worked 2 times...and now it is locking up again...either at the obsidian screen, or the press start screen.....grrr, nothing like wasting my money to purchase something that doesnt work