I sat for 5:30 minutes until my oxygen ran out.
OMG, that must have been the worst 5:30 minutes ever... asphyxiating right in front of the station. :O
I assume you are pretty new, so I'll try to explain it in depth.
In the "Outfitting" screen in the station where you buy new modules, keep a close look at the "power available" and "Power deployed". If you installed some power hog and haven't upgraded your power plant accordingly, the moment you press "u" (deploy weapons) in space, the power requirement will be the number in the second column. If that is too far above what your power plant supplies, systems will shut down, a big red warning will appear on the hud. Just undeploy the weapons, and you should be able to fly again.
Hint: If you are in the outfitting menu, bought a new item and hear the sound of a depleted shield reloading, you probably don't have enough power.
When you press "4" in the cockpit (not in the outfitting screen), you can go to the "Modules" tab and set the piorities, that is the order in which the modules shut down when you don't have anough power. You probably won't need a cargo hatch, FSD (It is inoperable while weapons are deployed anyway) etc. when in combat. That way you can install parts that are a little above what your power plant supplies, with varying results. I think in my ship, I can go ~1 MW above. In smaller ships it might be a little less.
And while you are here, there are also limits for your thrusters (if you go over the optimal mass, you won't be as fast or maneuverable as you could be) and your shields (hull mass should be below optimal mass, or they can't take as much damage).