Can't use su or sudo on Arch Linux

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http://unix.stackexchange.com – Sudo returns this error: sudo: effective uid is not 0, is sudo installed setuid root? And su - returns this: su: Authentication failure The user I'm using is a member of the following groups: disk wheel locate network video audio optical floppy storage power users I can log in to root, but can't elevate my user privileges, and I'm sure the password I'm giving to both is correct. (HowTos)