Some ideas :
- graphical issue with your settings;
- Administrative rights with W8. You'd better install the game out of C:\Programme Files or whatever its name is.
- Your firewall is blocking the game to prevent it to go on the network. Do a Ctrl/Alt/Del to see the prompt of your firewall asking what it should do, and/or go into your firewall interface, and add GP4 in the exceptions to communicate with network (local AND wan)
- ...