I am getting the same problem as http://forums.arcgis.com/threads/19468-Opening-tools-causes-ArcMap-to-freeze-crash
That is, when I open any geoprocessing tool in ArcCatalog (might happen in ArcMap as well, though it hasn't to me yet), sometimes the application hangs. The timing of the hang occurs after the tool dialog opens but before it finishes drawing. I don't know exactly what conditions cause this to happen, but it feels random, maybe in 1 in 4 attempts it hangs.
For me, terminating the hung process and trying again sometimes works, sometimes it doesn't. But it's a huge headache.
Has anyone come across the same problem and found any resolution? I have already tried reinstalling ArcGIS. I think this started happening some time after installing SP3 for ArcGIS 10.
Best Answer
My ArcMap was crashing every time I tried to open any geoprocessing tool, or the toolbox itself. Was working fine for a week, until I auto-downloaded some updates last time I shut down the computer. Then all of a sudden I couldn't open the toolbox without crashing the program. After a very frustrating 4 hours, I fixed the problem. Not sure if this is the same thing you are experiencing, but maybe it will help others:
I reinstalled ArcMap and Python after de-activating a virus protection program a co-worker had installed (avast free antivirus program, seems like a crap program). I think what had happened was the security software had prevented a critical file from being downloaded and installed during the automatic update which was preventing python from running properly within ArcGIS.