Changed the rad, engine light is ticking me off!

I need a little help. I am just learning about cars, (my car), and am having some problems. I changed the rad the other day, as it blew. Now, the engine light comes on after a minute or so, and I can't find a reason for it! The rad is full, and is flowing nicely. All other fluids are topped up and the car seems to be running fine.

The thermostat seems to be working. When the car heats up, the fan kicks in like it should, and cools down just fine. Could it be that I knocked a few wires out of place, or should I maybe think about changing the thermostat?

Any help, would be greatly appreciated!

Thanks!! :)