I accidently deleted my /Volumes folder. What can I do to get it back? USB's don't show up, dmg's don't work and more stuff like that. Please help!
1) Restore from a time machine backup, if you have one
2) Reinstall Mountain Lion from your recovery partition:
Start from the OS X Recovery System
Recovery System or Internet Recovery
You could recreate the directory via terminal, but this would be a makeshift/messier solution, in my opinion.
Retrieving data ...