Over the past month I have noticed a gradual slowdown in my late 2012 iMac. Symptoms include slow loading of applications, freezing up of apps, and extremely slow boot up times. Last night I went to launch an application and it would not open. I restarted the computer and it took approximately 15 min. to get to the log in screen. I attempted to boot in safe mode and run disk utility. The program was unable to complete the disk check and put up an error message. I tried all the normal remedies with no success. I attempted to boot the computer while holding down the command+s and run "fsck -f". The process was unable to complete and returned an error of "disk0s2 I/O error" I logged out and attempted a reboot. This time the boot process took nearly an hour and I was unable to get to the log in screen at all. My final attempt to boot up ended when the progress bar got to about 2/3 the way across and the computer would shut down completely. Any idea what could be causing this and if so what are my best options to get my computer back up and running. Thanks!!