Hey Trabzed, apologies for the late reply!
As mentioned above, ensure you meet the requirements. If you do, please verify your game files:
1. In Uplay, click on Games tab at the top of the window
2. On the next screen, hover over the game tile. This will make a little arrow appear at the bottom right of the tile
3. Click on this arrow to make a drop-down menu appear, then click on Verify files
If the issue persists, please perform a clean boot and test again.
If the game STILL wont open, please let us know!