I had a recent post (http://www.charleslabri.com/?p=43) about SharePoint 2010 installation woes, I had the same problem crop up. This time it wasn’t the registry. I combed through the registry with a fine toothed comb. This time it turned out to be simple.
Looks like windows updates were pending, though somehow the windows update informational was not present.
When installing software I would get the error that there was a pending install.
Something like this,
“Setup is unable to proceed due to the following error(s):
A system restart from a previous installation or update is pending. Restart your computer and run setup to continue.”
It linked out to Technet with an article talking about what prerequisites that SharePoint had. How unhelpful.
Rebooting didn’t solve it, and searching through the registry didn’t solve it.
It needed a full shut down, and then a manual power on. Looks like windows updates are picky.