Program doesn't open

I have ArchiCAD 8 installed on my computer for some time and it was working fine until now. It simply doesn't open. It shows that it's loading, the window appears but after that, it shuts down. I didn't changed any settings, I don't know what's the problem. I also re-installed the program, still no result. Maybe you can help me.

How are you launching it? From a NEW desktop shortcut or Start>All Programs ?

I launched it in the both way but it is the same: doesn't open.

Are there any coloured flags showing in Admin Tools>Event Viewer?

From where can I access Admin Services>Event Viewer?

cp->admin tools->event viewer
there you'll see sublists:
system
applications
security

nevermind, thanks anyway guys but I chose the ultimate solution: reformatting my PC and reinstalling Windows XP. Now everything is back to normal but I have a lot to catch up.
:)