OK, I've got this problem again, only this time the problem only seems to affect Firefox and Thunderbird. Rebooted several times. Tried resetting to the last restore point, but that didn't work. Tried setting a new Firefox profile, and that didn't work either.

The symptom is that you click on the Firefox or Thunderbird icon, the process appears in the Process Explorer list, but the window never opens.

Curiously, if Firefox has been "started" this way, Internet Explorer hangs starting until I kill the Firefox process.

Any ideas? I suppose the next thing to try is uninstalling and reinstalling Firefox/Thunderbird, but this whole thing is getting old.

The box is a Sony Vaio running Windows Vista. It was completely restored from scratch less than two weeks ago, after the last fiasco. (I'm suspecting that my aborted install of Acronis True Image may have mucked things up this time.)

Sigh! Another symptom:

It occurred to me to try printing something, but if I open "Printers" it just sits there "searching".

So something is rotten in the bowels of Windows.

Minor update: It occurred to me to kill Internet Explorer (where I'd attempted printing). Then Printers comes up fairly quickly -- with no printers defined.

Clicking "Add a printer" does nothing.

Update: Well, following this suggestion to stop and restart the print spooler brought the printers back.

And, wonder of wonders, Firefox now starts OK. Stopping and restarting the print spooler!!