Using 10.1, both SP1 and no service pack, I'm getting blank windows when I open the GUI dialog for any geoprocessing tool from the ArcToolbox. The Environments window is also blank. Tool help windows open up and display fine. Tools are there, as I can use then via the Python window, but no GUIs. I think the content of these windows is written in html and xml, and I've located those files in my system; they're being written dynamically, I think, to suit whatever tool I tried to open last. Yet the window where I can normally specify tool inputs remains blank, both in ArcMap and ArcCatalog. Started doing this suddenly, after a bunch of custom script tool runs the other night, and a few I had to force-stop mid-way (which never caused this before). Simply restarting my system didn't work. Any insight appreciated, thanks!