Lion not booting

Hello everyone. I've been a Mac user since 2007. To describe the problem, it begins with me being a MobileMe user which brought the following: I needed to "migrate" to iCloud.

Although I still have a few months until my subscription has ended, I'm getting ready for the migration and, also, I couldn't wait to try the new OS X (since iCloud only works in Lion).

My Mac Mini being a 2,1 (the 2.0GHz Model), I got hardware ready (installed a 320GB HDD and a total of 3GB of RAM) and bought the Lion software from the Mac AppStore. The installation went flawlessly, it rebooted and I got ready to use it.

However, when I rebooted a second time, I got stuck at the Apple logo and the spinning wheel. I let it still for more than half an hour and it keeps spinning. I shutted it down and powered it up again and worked. Even still, everytime I reboot or power the computer, I still get this problem. I've used the Command-R action before booting to go to the system's Disk Utility (as opposed to the desktop one, I don't know if there's a huge difference) and Verified the disk. I fixed the existing problems twice and repaired the permissions. What bugs me is that the pemissions are never fixed, although it says that they are. Every time I push "Repair Permissions" I get the same files being fixed from the last repair.

None of this has helped me and I am still facing these problems. How can I fix this?

PS: I've been using the 320GB HDD with Snow Leopard for some months and, eveytime I checked, there were no problems.