I've got (I think) an late-2009 Mac mini. (It's the last mini before they removed the optical drive)
Recently it crashed, and when trying to reboot it, it hangs at the Apple logo.
When it first comes up, there is a progress bar at the bottom and at spinning "wait" icon. The progress bar goes away, but the wait icon remains indefinitely (I let it sit for 4 days).
I've inserted a USB stick with a Lion recovery partition installed on it, but when I press ⌘ + R after pressing the power button, I get the exact same results as above (i.e., it does not boot into the recovery partition, but instead shows the Apple logo, progress bar, and wait icon).
I know there should be a recovery partition on disk, but if that disk has failed, I'm hopeful that it would still launch the recovery partition off of the USB drive.
Am I missing something simple, or is this expected behaviour with a failed disk?