If you use sortmirrors while something goes wrong, like dns resolv doesn't work, sortmirrors will choose 0 out of the X servers found in the file. This renders pacman broken, as it doesn't have any mirror left to update, even after the network problems itself were solved.

Workaround: delete affected mirror lists by hand, then do pacman -S pacman, hopefully pacman package is in cache :)

Another thought: It seems dns went down everytime sortmirrors was run(?)