My macbook pro (late 2011) has been running very slowly for the past day or two. When it froze this morning, I force shut it down by holding the power button. When I tried to turn it back on, it would get stuck on the gray apple logo and not boot up. I went to this guide for help: http://support.apple.com/kb/TS2570. Tried to boot in safe mode and I got a repeating disk0s2: I/O error that looked like this http://imgur.com/HJVbtL7 (apologies for poor quality). It just kept repeating, so I tried resetting NVRAM and still nothing. The gray apple screen seems to vary, also - sometimes I got the scrolling load cursor, sometime the cursor was frozen, once or twice I got the regular point cursor that I was able to move around, once I got a progress bar that returned to the scrolling cursor after it loaded. I have no idea if that means anything. So next I went to disk utility, it found an error (something about having 200 something files instead of 184 files, along those lines) and repaired it, got the green "this looks okay" message, tried to reboot and got stuck again. Checked safe mode again and it still showed the long list of disk0s2: I/O errors. Repeated the disk utility process - the same error it displayed before appeared, it repaired it again, and it gave the green okay again. I don't know how the error reappeared when I rebooted even though disk utility indicated it had successfully repaired the issue. Currently in the middle of backing up with disk utility - I will try rebooting again, but I'm assuming I'll still get stuck at the gray screen. Is there anything else I can try before I reinstall? And does this indicate a hardware issue or something else?