When the windows logo appear, hit F12 (most PCs use F12, yours might be different). A menu should appear, go to settings/display (or find something similar to that), then change the settings so that it uses the dedicated GPU. Every bios is different but they all should have similar options like the ones I mentioned. And, like Ripley said, make sure your monitor is connected to the 7770 itself, not the onboard.
EDIT: I'm on Vent, hop on.