You have two placement issues (sats and sub).
For the sats start with them as far apart as they can be. You can aim them towards you or straight ahead. If you don't get sound from the center then move them closer together.
For the sub your will get the most output if the sub is as close to a corner as you can but the bass will be uneven and boomy. It's a trade off. Try different locations around your PC area readjusting the level at each location. If you have EQ available on your PC that can be used to help flatten tubby bass but you have to be very sparing in boosting bass as it can add distortion.