I'm sure WEI says that your screen may flash during testing, but if you can't play Watch_Dogs then it sounds to me like a hardware or potential driver problem.
Did you make sure you plugged the two PCIe 6 or 8 pin power connectors into the Graphics Card? Without them you won't be able to game and will probably only have enough power to run the basic desktop. Also make sure that you did fully insert the card into the PCIe slot, there is a clip at the back (towards the inside of the case) that latches into a notch in the Graphics Card Circuit Board.
Step 1: ensure the bracket on the GPU with the DVI etc sits flush against the back of the case is flush with the back of the case.
Step 2: ensure the latch on the PCIe socket is latched in to the notch on the card, if not then gently push or wiggle the card in the slot to get it all the way down, but DO NOT PUSH TOO HARD ONTO YOUR MOBO, the last thing you want to do is break something else.
Step 3: ensure you plugged the PCIe 6 or 8 pin power connectors from the PSU into your card.
Step 4: once you have ensured everything is fine physically, get something like MSI afterburner that comes with MSI Kombustor to do a stress and stability test on your GPU. Since you have a GTX770 I would open MSI Kombustor from Start>All Programs>MSI Kombustor 2.4 and select Furry and Tessy Test (GL4), then go to settings and change the resolution to 1920x1080, then run the test. This puts more load on my system than Watch_Dogs does and I have a GTX470.
If you get a black screen when you start the stress test and your screen comes back on and Kombustor has crashed and you get a message from windows saying the "Display Driver Crashed and restarted" then you either have a faulty GPU or a driver problem.
