System Event Notification Service doesn't start - can't escalate to Admin

"I've made some progress in this.

In Safe Mode's command prompt, I've disabled UAC.

reg.exe ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v EnableLUA /t REG_DWORD /d 0 /f

Now I can run setup.exe off the Win7 setup disk as admin, and should be able to repair (by doing an ""upgrade"") my installation.

Having disabled UAC, I still couldn't get into the Computer Management window, it failed with an ""Unspecified Error"". I managed to run mmc.exe and attach compmgmt.msc, but I still couldn't into the Event Viewer, because the service wasn't running (and wouldn't start when I tried).

So now I'm going to do an ""upgrade"" and see how that goes."