I have a problem with QGIS 1.8 with OSGEO4W installer (windows 7 - 64 bit). QGIS crash on startup, it shows the splash screen and then nothing. I have updated from an old 1.7.4 QGIS version. I have done the same procedure in a portable computer and it works fine. The problem is only in the workstation. Is there a log file to view what is the problem? Thank you
Today i stumbled on the same problem (Win 7 64-bit, QGis 1.8.0). In search of a solution i disabled all plugins (in the registry), deleted the .qgis folder, Qgis registry entries and reinstalled, but nothing helped. However, i had QGis working just fine about a week or two ago. My QGis was crashing when the splash screen displayed "Starting python" (or something similar) and i remembered that i recently upgraded from Python 2.7.2 to 2.7.4.
So, i reinstalled python 2.7.2, changed environment variables to point to python 2.7.2 and now my QGis works again. Check your python version, you might have the same problem.
You may have to delete your .qgis folder. Usually under c:\windows\users\. See also: https://gis.stackexchange.com/a/57335/3438
I had a similar issue and I just solved the issue with Nathan W (a real Guru!). I had a file called path.txt in my c:\ and this caused QGIS-Dev build to fail (Lisboa worked fine though).
Just rename the file (c:\path.txt) if it exists. Also install OSGEO4W in admin.
See QGIS Dev install issues for details.