Mac mini starting in Recovery Mode

I left my Mac mini on for a couple of days. I thought I had shut it down, but when I went to do some work, it had a white pin wheel running. The computer was not responding so I powered it off. When I turned it on it started in Recovery Mode. I ran Disk Utility, says everything is OK. I tried reinstalling OS X, but only gives me the Recovery Disk as the install location. I tried resetting the the PVRAM, doesn't work. I tried a Time Machine Backup, won't work. I tried Safe Mode, Safe Mode with Verbose - nothing. What else can I do?