My MacBook was going really slow and I performed a forced shut down because it kept freezing. When I tried to start up again, it wouldn't boot past the Apple logo and the spinning wheel. I was told hold command, p, r and control while restarting could fix this so I tried. After that, the computer suddenly shut down shortly after getting to the boot screen. Disk Utility won't work because it shuts down before it loads. Same for safe mode. It works in single-user mode and fsck returned the following: disk0s2: I/O error. Invalid node structure (4, 0) Invalid B-tree node size (4, 0) Invalid node structure (4, 0) Invalid B-tree node size (4, 0) ** The volume could not be verified completely. /dev/rdisk0s2 (hfs) EXITED WITH SIGNAL 8 Any help with this would be greatly appreciated.