Don't worry about resetting PRAM. It has absolutely nothing to do with your problem. Neither does restting the PMU/SMC.
Here is what I would try. First, boot up in Single User Mode and run fsck.
1. Power on Mac while holding Command + S
2. When the prompt comes up, type in /sbin/fsck -fy and hit Return
3. After it is done, then you can hit return to finish booting. Basically this is running a Disk Utility style repair on the drive before booting the Finder.
You can do this if you can't use the recovery partition for Disk Utility (10.7 and later which you should be running on a 2012) or you cannot boot the Mac off your install CD and run it from there. You can boot to the recovery partition by holding down Command + R when you power it on.
If that doesn't work you may need to try some 3rd party program to fix the drive.