there are hacks you can use to get the (sam?) file with the password (i assume thats what you mean or is your system simply unstable..?)
Also, do you have the "guest" enabled?
is it pro or home?
do you see the "welcome screen" when you log in?
if all else fails, a good reformatting could work... however i can empethise with you in how you wouldn't want to lose your files (like the all the simpsons episodes....)