Using my laptop as a gaming screen for ps3.

That HDMI port is output, not input, so that will not work.

If you open your laptop case and find the wires that go from the mobo to the screen, and then cut them, and splice them into an HDMI cable then you can hook that up to your PS3, but unless your monitor is 720p or 1080p, or has a very good scaler in the screen, then it will not work well.

In short... no, you can't without ruining your laptop.