I've been using Sigil, a free ebook editor, for some months on XP.
A few days ago it stopped working.
If I start the program, I see the process start, then a second later exit, never opening a window.
I uninstalled it and reinstalled. Same.
I deleted all its temp files and storage.
I tried Safe mode.
I tried the Portable version.
Turned off my antivirus and firewall.
Same.
I may have installed a Windows update (the last one, presumably) since the last time it worked.
You can try the portable version from here:
http://www.softpedia.com/get/PORTABLE-SOFTWARE/Authoring-Tools/X-Sigil.shtml
I guess one of its dependencies is not found or is the wrong version, but no idea how to work out what, I can't find any error messages.