windows update failure and the error is 0x80070420.It is requiring me to register or reinstall the files
Go to My Computer and from the Tools menu, select Folder Options then View. Scroll down to "Show hidden files and folders" and tick that. Further down, untick "Hide protected system files" then click Apply, accept the warning and OK your way out. Navigate to the C:\Windows folder then to Software Distribution. Choose Select All from the Edit menu and hit eth Delete key. Next, go to the Event Cache folder and do the same. In the main Windows form, you may as well also delete all the blue files starting with a $ symbol and which are historic Update files and uninstall information you no longer need.
You will have gained as much as 2Gb hard disk space and the update will wander in again in its own time and probably install properly.