So today my MacBook Pro (2010 model) was acting weird when I was bored and changed my MacintoshHD to no use for everyone. My profile still had read/write capabilities. It wasn't frozen but it was spinning the beach ball for like 5 minutes. So I restarted it and walked away. I came back and it was stuck on a white screen with the mouse pointer in the top left corner with the apple logo in the middle. I did a safe start, although I'm not sure if I let it sit long enough. I did the command-option-p-r start with no avail. I also just did the command-s start and did the fsck -fy and return. It went through its thing and it said that MacintoshHD was ok. I typed reboot. And it's still stuck at the same screen. I do not have a backup and don't have any boot discs with me.
You messed up to say it politely, I am pretty sure you changed the R/W on the disk, well, if that is the case the Mac will never start up.
If you change it to read only the system can't write to the disk, this means it gets stuck.
There is a way to make it startup again but then the system is not secure anymore since you will change all the files folders to R/W for everybody.
You can do so by booting into Single User Mode and then mount the disk and then enter a command so that all permissions are set to R/W.
What might help is to repair Permissions on the disk with Disk Utilities run from an Installer CD/DVD, if you have one, but chance is it won't work, last time there was a guy with exactly the same problem and could only "Fix" it by entering those commands in Single User Mode.
The below instructions should work but I am not 100% sure so be careful.
To boot into single User Mode hold Command-S at startup.
To mount disk enter:
fsck –fy
mount –uw /
Then enter:
chmod ugo+rwx /
Edit: after you have done this Open Disk Utilities and repair permissions on disk, and see if it repairs the files.
