A straightforward resolution for the "User Profile Service failed the logon" error.
1. Start Windows in Safe Mode.
2. Open Registry Editor.
Click on the Start Button>Type "Regedit" on the "Start Search" box (for XP you need to click on "Run" then type "Regedit" on the box) then hit enter.
3. The Registry Window should open. We then proceed to look for this particular registry key:
HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>WindowsNT>CurrentVersion>ProfileList.
We should see a list of folders, we need to look for the ones that starts with : S-1-5-.
There should be two folders with a similar name although the other will have a .BAK on the end. We should now rename the other folder without the .BAK on the end by adding something like .OLD on it's end while removing the .BAK from the other.
4. We now then close the Registry Editor and restart our computer normally.
5. After doing so we should be able to login normally using our profile.
Simple as pie. ( ^_^)
