After updating Emacs to 24.5.1 (from 23.2) on my Windows 7 machine, I found that Emacs wouldn’t startup properly and would just display a white/blank screen and appear to hang. When running it from the command line, I was seeing a couple of lines of errors indicating a problem with GTK on startup:
GLib-GObject-CRITICAL **: gtype.c:2720: You forgot to call g_type_init()
GLib-CRITICAL **: g_once_init_leave: assertion `result != 0′ failed
This reminded me that I had installed GTK+ 3.0 recently prior to my update and thought perhaps this was some interaction with the new GTK installation. Rather than uninstall GTK, I opted to remove the path to the GTK bin from my Windows 7 PATH environment variable. Once I did that and then tried to run Emacs, it worked properly. Not sure what the weird interaction was about — perhaps the wrong GTK DLL was being loaded up?