First log in as Administator. You can try the following in any order or combination to see if any of them works (hope at least one works).
(1) Disable Fast User Switching (Start, Control Panel, User Accounts, Change the way users log on and off, and untick fast user switching). This is not a bad idea anyway as this feature uses a lot of computer resources.
(2) Disable the Welcome Screen (same as above, untick the box for the Welcome screen). You will switch back to the old Windows logon screen. Also, if you turn off the Welcome Screen, you cannot use Fast User Switching.
(3) Change the settings of the Security Log in Event Viewer.
Start, Control Panel, Performance and Maintenance, Administrative Tools, Event Viewer.
On the left, find Security Log and highlight it.
I'm not familiar with XP Home, but I've read that by default, XP Home is set to audit logon events (success and failure). If this is correct, the right hand pane should show a long list of logon events.
Right click "Security Log" on the left and select Properties.
Under the General tab, in the "Log Size" box, the default settings should be 512KB and "Overwrite events older than 7 days". Change that to "Overwrite events as needed". Click OK if you're done, or click Apply to go to the next suggestion.
(4) Select the Filter tab of Security Log Properties, if you have the tab. Untick Success and/or Failure. Click Apply or OK.
The success/failure log is for you to keep track of logon events, to see if there has been unauthorised access or attempted access to your computer. In a home computer context, and if you have set up limited accounts, this is not really important. You've probably never looked at it.
Hope some of these steps work.