Are you logging on as administrator or a user with administrative access,there is a difference.
To Log in as Administrator:
If you want to log in as Administrator, but it is not shown on the Welcome screen,
Hold the Ctrl-Alt key and press Del twice.
This will bring up the normal login and you can log on as Administrator
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To unhide the Administrator account so it does show up:
Start Regedit
Go to HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ Winlogon \ SpecialAccounts \ UserList
Unhide the Administrator key by giving it a value of 1
You could also try safemode
Also,when you get to the option to update say no,you can update later.