yep ive had a couple games turn up with the center cracked recently, and so has my friend, and as makelith said its from how we were pulling the games out of the cases, we wouldnt notice until taking the game out of the console so at first i thought it was the console doing it, then i found out it was me. I lose halo 3 and ninja gaiden 2 to that.
As for the videos.
1. are you playing them in the same console you downloaded them on, or are you downloading them, then putting the HD into another xbox and trying to play them, this wont work because of the way xbox signs its downloads, it will only play on the original console it was downloaded on, just like all other files downloaded from xbl.
2. are they rented movies? because those expire after your first full watch and or the expiration date. any paid for video on XBL that i have seen, does expire.
3 drive is dead? dont wanna mess with MS? no prob, Ebay. get a new drive of the SAME model and number, take the PCB board off the old drive, and replace the one on the new drive with the old one, pop it in your xbox and go. I just had to do this because i broke my old drive when i took it apart lol