We'll be editing two registry keys. One in the Machine hive and one in the User hive.
Click Start, then Run, type regedit and click "Ok".
In Registry Editor, expand (click +) HKEY_LOCAL_MACHINE, then SOFTWARE, then Microsoft, then Windows, then CurrentVersion, then Internet Settings, right click on 5.0 and choose "Export"...name this file 5.0.M.old and save it to your desktop. Expand 5.0...then right click on User Agent and choose "Delete"...accept the change.
Collapse this hive by clicking the - sign next to each expanded key.
Then expand (click +) HKEY_CURRENT_USER, then SOFTWARE, then Microsoft, then Windows, then CurrentVersion, then Internet Settings, right click on 5.0 and choose "Export"...name this file 5.0.U.old and save it to your desktop. Expand 5.0...then right click on User Agent and choose "Delete"...accept the change.
Collapse this hive by clicking the - sign next to each expanded key. Close Registry Editor and reboot.
Try Windows Update.