how do I remove erroneous user name in windows login?

Windows 7 is giving me trouble. Initially, I had been running with only one user account. Originally I believe it was named "pob" (not important). A few years ago I changed the name to "D830-laptop" and ran this as administrator.
Recently I was enlightened to the problems that could arise if running all the time as administrator, so I made new accounts on all of my PCs. I went to my laptop and created a new account and named it "joe" (fictitious) and gave it administrator privileges, then changed the D830 account to standard user vice administrator. This seemed to work well on my other PCs, but when I did this on my laptop, I came up with something unexpected. When I rebooted the system the Windows logon screen came up with the original "pob" username and said that the password was incorrect. Long story short, I cannot find any user account that is labeled "pob". How can I prevent windows from trying to bring this account up? My administrator account is password protected, but the D830 account is not because it is only a standard user account (now). Is there some place hidden that would have this info? Any help would be greatly appreciated. Thanks. I hope that this was clear enough to understand.

Don't know if this will help you, but I found that if you rename an account it does not really rename it. It only creates some sort of link between the new name and the old. You can see this if you look in the file system by means of Windows Explorer and see that your files are still under the old name. So the old name is still lurking somehow.

Given that when you first use Win7 after installation the first account you create has administration power, it is best to call it something that is clearly administration and use a name you are going to keep. Like "admin" or "superman". Only after that, create your normal user account as " Joe". This is not intuative - one is inclined to create the "Joe" account first.

I thank you for your response, but I do believe that the user name was indeed changed. I have looked in most of the hidden files that I could think of (NTUSER, registry userprofile, etc) and everything shows the user profile as D830-laptop. I did find a few items in the registry user profile that showed two other user names. One was c:\Users\NeroMediaHomeUser.4 and the other was c:\Users\temp laptop name. I'm not sure if these are necessary or maybe part of the problem, but I left them alone (for now). I even ran a program called Registry Clean Expert that I have had for years. It cleaned up a lot of unnecessary files but failed to fix this issue. I don't want to go back and start fiddling with changing user/admin accounts. I like the set up that I presently have with the exception of the logon screen showing a defunct account. I do appreciate the suggestions, though.

I don't have it set to auto logon (yet). I was getting ready to try that when I looked in the registry once more to see what I could find. Lo and behold, I actually found the default domain name and default user name. It was in [HKLM\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon]. I also found (in the registry) the logonUI defaults in [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI]. This one shows last logged on Provider, last logged on SAM user, and last logged on user. Don't know if I should modify these or not. Any suggestions?

In user accounts it shows two accounts plus guest account (which is off). Both accounts are the ones I made recently (the D830-laptop, which is a standard user acct and the Joe, which has admin privileges). I also turned on auto login for the standard user account. This seems to be a good fix for now. When I boot up, it automatically opens up the standard user acct without bringing up that issue I had before. Now if I want to switch users, I can do it normally through the start button. Thanks for all your help.