Why is my MacBook Pro frozen?

Press and hold the Power button until it shuts off. It takes several seconds.

No idea why it froze. It might never happen again. If it does try to correlate the freeze to something you were doing - obviously if it was Skype it would appear something is wrong with Skype.

Three ways. Click apple logo located at the top left of the menu bar and select force quit. Hold down the option, command, and escape buttons and select force quit. Hold down the power button untill the computer turns off.

JamaicanBMW's case seemed tied with the Skype update. In case anyone else has a similar problem but restarting doesn't fix it, here's what worked in my case:

I had a problem with my MacBook Pro 13" (2012) when the keyboard and trackpad stopped working for seemingly no apparent reason. I discovered that if I plugged in a USB keyboard and mouse, those would work.

When I consulted with Apple Care, they had me reset the PRAM, which did the trick for me. From what I understand, the PRAM is memory that the computer uses to keep basic display and input preferences and info, even when the computer's turned off.

Weeks ago I had installed a 3rd party mouse and keyboard. Even though I wasn't using them when the problem happened, Apple Care said maybe the software accidentally interfered.

To reset the PRAM, I restarted the computer, and when the apple screen came up and the chime happened, I pushed COMMAND+OPTION+P+R (four keys), and waited for it to re-chime a couple times. Then the keyboard & trackpad worked again! See the About NVRAM & PRAM page for details.

Might not be a cure-all, but it helped in my situation.