Try this before you re-install windows, ONLY if you are NOT on a network.
1.In the Control Panel open "Network".
2.Then remove "Client for Microsoft Network" and/or netware network if they are there. On a stand alone computer you need just Dial up Adapter and TCP/IP network components installed.
3.You could also remove/disable "File and Printer Sharing".
4. Re-boot and the password window should not appear.
If you are networked then after step 1 above, select "windows logon" as the primary network logon. This may bypass the logon window.
Hope it works
Derek