First of all I took everyones advice from last week:
Ran the free TrendMicro Hijack and rootkit finder/killer, no problems found
Ran a full scan using both Avast and MalwareBytes, no problems found
Ran the msft system upgrade compatibility tool (kb947821), some problems found with an old installation of office 2010, but nothing that would affect MSIE
Ran the automated WMI diag tool from msft and wmimanage /verifyrepository, some WMI problems found with the same office 2010, again nothing that would put the zap on MSIE
From an elevated command prompt, I ran the following one-liner I found on another forum from a user called 'archer'. This did the trick
FORFILES /P %WINDIR%\servicing\Packages /M Microsoft-Windows-InternetExplorer-*11.*.mum /c "cmd /c echo Uninstalling package @fname && start /w pkgmgr /up:@fname /quiet /norestart"
This apparently cleaned out a borked / aborted install of IE11 and rolled back to a previous, functioning install of IE8 (the factory default for Windows 7).
Rebooted, verified that IE8 was still functional.
Kicked off a fresh install of IE11, that ran fine, pointed the machine at MS Updates, those ran fine.
We're going to run this on a similar machine in a test environment next week with a registry trace tool running to see exactly what it going on under the hood.
Thanks to everyone for their help last week.
Edited by newsposter, 14 June 2014 - 03:57 PM.