I forgot to mention running fsck in Single User mode. Safe Mode is supposed to run fsck but you indicated no success.
To enter Single User mode restart the mini while also holding down the Apple key and the S key (before the bong sound). You should get a bunch of text and then a command prompt. Below is from Apple's support page
http://support.apple.com/kb/ts1417:
At the command-line prompt type:
/sbin/fsck -fy
Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:
** The volume (name_of_volume) appears to be OK
If fsck found issues and has altered, repaired, or fixed anything, it will display this message:
***** FILE SYSTEM WAS MODIFIED *****
Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
When fsck reports that your volume is OK, type reboot at the prompt and then press Return.
Your computer should start up normally and allow you to log in.