Laptop Monitor Not Enabled?!

I was using a second monitor for my laptop, with the actual laptop monitor disabled. I thought I re-enabled the laptop monitor and disabled the second monitor before I unplugged the laptop to take with me to class. It turns out, I didn’t!

Both monitors are disabled, I’m using an old PC right now to do this. Even when I plug the second monitor into the laptop, there is no signal, it does not work. The laptop monitor does not work. It is a blank screen.

How can I re-enable either of the monitors?

I’m using a Sony Vaio PCG-K23 running on Windows XP.

Please help!