QUOTE(BigBadBruno @ Mar 3 2008, 08:08 AM)

This all seems really weird to me. I recently purchased a new 360 just to get the HDMI capabilities. I plugged in my old hard drive with all my arcade games on it and they work perfectly fine. I also bought a 120gb hdd later and transferred everything over to that. Still everything works fine. Take your hard drive to a friends house and try it out on their xbox. See what happens, then you will know if it is specifically the 360 that you own.
This is more then likely because you are connecting to Xbox Live with the account your purchased the games with...
NOW, for everyone else. You can get your arcade games re-signed for your new 360. But if you have a lot of arcade games (I have about 30+ ... my post RRoD xbox is on it's way back from texas right now) it'll take a bit of time.....
(From the major nelson podcast ... 2 episodes ago. I haven't tested yet, but i'm sure it works. Sorry if i get anything off, just typing as I'm listening, No show notes.)...
Sign into live with the original gamer tag that you bought the content with, go to Xbox Live Market Place, Go to Account Management, then "Download History". Then you can then select "Download Again", and then it should re-sign for your new console.
Unfortunately, it sounds like you need to do this for EACH title, but it's better then nothing I suppose.
Have fun kids.