I have been using my pc for quite some time with no problems. I was able to shut it down and restart it and have it go straight to my desktop without having to type in a username or password. Now for some reason, I restarted my computer and it now pops up asking for a username and passord. I dont have a username or password.

I am on a friends pc now trying to get assistance......what has happened to my windows xp that I now need a user name and password? I am unable to do anything because of this....PLEASE HELP.

Assuming you have physical access to the machine (ie: you can boot a floppy or cd-rom) then you can 'root' your machine and get full access to it. There are six different methods that can be used to achieve this.

1. Go to: [http://home.eunet.no/~pnordahl/ntpasswd] This method is a boot floppy or CD to reset the password. I've used this successfully a few times, on a NON-domain account. If you plan on using this at home, then odds are likely you will be OK. If you plan on using this at work, you should know if you have a domain or not. If you do, there are some more instructions (in the url above) to get past the domain controller. If you fail to follow those instructions you can alter login information badly enough such that you will need to reinstall Windows to get back in.
2. Re-install Windows, but don't format the hard drive and choose to use 'c:\Win2' for the windows directory (or some unique directory). This process will allow you to keep your files intact but will NOT keep your programs intact. After doing this, it is highly suggested to do a formatted reinstall.
3. Use Windows XP recovery console to manually go in to c:\windows\system32\config and delete the SAM file. Someone at Experts-Exchange posted this question: [http://www.experts-exchange.com/Operating_Systems/Q_20881463.html]
4. Use winternals ERD commander to blank or change the admin password. [http://www.winternals.com]
5. You may also try this - [http://support.microsoft.com/default.aspx?scid=kb;EN-US;308402]
6. Windows Expert Password at: http://www.atlantisminds.com/

If you have the user password to login to windows xp or nt, you could use a more easy way to get in. As long as you know the administrator username and password you can press Ctrl+alt+del and del again on the windows login screen. Then, follow these steps:

1. Type Administrator in the username field.
2. Type the administrator’s password (or the password you set up during the installation of Windows) in the password field. It might be a blank field as well.
3. Go to control panel > user accounts and change the user's password.