I have a late 2012 iMac running osx 10.8.5. I keep losing access to my internal hard drive. I can reboot and regain access and it will last for a few minutes or hours. Disk utility does not seems to help.

I have a late 2012 iMac with an I5 precessor running OSX 10.8.5 and a 1tb internal hard drive. I keep losing access to the internal hard drive/startup disk.
I can reboot and everything operates as normal for a few minutes or hours but then I lose all access again to anything on the hard drive. The computer is still up and running but no files can be accessed and certain websites cannot be acessed even though internet access appears to be normal. Disk utility can only find permission errors related to iTunes which can be repaired only to come back at the next scan (I would not think permission errors would have anything to do with the hard drive crashing). It does not seem to matter what program I am using at the time access is lost and it can lose access sometimes right after reboot when no program is running.