Do you mean the Welcome Screen?
The computer doesn't usually forget passwords unless the user's profile has become corrupted or virus infected in some way.
If either is the case then we can use our backup Admin user account to sort out the problem. Has your friend tried that yet?
I'm trying to help a friend with his computer. Unfortunately I don't know much myself. When the computer is turned on it comes up with a blue screen saying enter password, but when he puts his password in it says invalid password. Either he has forgotten his password or the computer has. How can we get windows running, preferably without a password?