360 game freezes after 15 or less minutes

[Racecarlock]

So today I cleaned my original IV disk with isopropyl alcohol and a q-tip using the technique outlined everywhere (sweep outward, don't circle). Then I waited 30 minutes for it to install on my hard drive. First problem, the game conveniantly forgets to load the elevator markers that are supposed at playboy mansion, the location I saved at and prefer to save at, because it's awesome. So I had to use the fire escape to get off of the roof. Second problem, it froze after about 10 minutes of driving. What the f*ck is going on? There were no problems during installation. Why does it freeze? Why does it forget elevator markers at safe houses? Seriously, I want to know. Original IV isn't my favorite GTA, but I paid 60 dollars for one new and my mom had to buy the used copy I have. I need some help here.