Your "old" account may have been the Windows default administrator account which cannot be deleted and should not have been renamed and used as your account to start with.
The MS Knowledgebase below shows you how to repair the profile connected to the account:
Windows XP Problems if Your Profile Is Damagedhttp://support.microsoft.com/kb/326688/en-us
"The Administrator account is created automatically when you install Windows XP. The Administrator account is the one you use when you first set up a workstation or member server. You use this account before you create an account for yourself. The Administrator account is a member of the Administrators group on the workstation or member server. The Administrator account can never be deleted, disabled, or removed from the Administrators local group
, ensuring that you never lock yourself out of the computer by deleting or disabling all the administrative accounts." - Microsoft