Well I haven't read this anywhere else so I am just going to say it.
I, as many others, have been having problems with getting O2 to start. My main problem was that O2 won't start at all. It never can up with an error or anything. Well I found the solution. This is however only a solution if u have XP. For the other OS problems I have no idea.
Make sure the compatibility mode for the .exe file is set to Windows 98 / Windows ME. If u don't know how to change it, right click on the .exe file or shortcut and select Properties. Then select from the menu on top Compatibility and check the box "Run this program in compatibility mode for:" and hopefully u will be good to go.
If this does make your O2 start then good. If it only starts and then nothing check
http://ofp.gamezone.cz/_hosted/brsseb/tutorials/start/start.htmHope that helped some of u.