If your system contains certain sound cards (Dell Inspiron 3500 ) you can end up with a locked system that can only be edited from a rescue mode. The problem is that sndconfig edits /etc/conf.modules before it tests if your system has a working sound card. On installing module it can crash the system. If you reboot you cannot get around the modules being loaded even if you do a linux single because of /etc/conf.modules syntax. Suggested Fix: a) have sndconfig test modules via explicit insmod commands and at end of run write /etc/conf.modules b) have initscripts not load sound modules in single user mode
FWIW, sndconfig does tell you it's writing a new conf.modules. :) Boot with "linux nomodules"; alternatively "linux init=/bin/bash".
*** This bug has been marked as a duplicate of 5429 ***