on a crash your profile may have been backed up
incorrectly, preventing you from logging back in.
default profile folders may also be missing
to correct, navigate to profiles in regedit:
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
back up your profiles 1st
edit rename copy & correct each profile entry
that could either be missing or renamed as .BAK
references
article
windows7 forum
microsoft knowledge base
fix a corrupted profile
