mac book pro is not opening up. its stuck on gray page with circling thing at bottom of page

I would recommend Restting the SMC and Resetting the PRAM as possible cures:

Resetting NVRAM / PRAM

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

Resetting the System Management Controller (SMC)

Resetting the SMC on Mac portables with a battery you can remove

Note: Learn about removing the battery on MacBook and MacBook Pro.

1. Shut down the computer.
2. Disconnect the MagSafe power adapter from the computer, if it's connected.
3. Remove the battery.
4. Press and hold the power button for 5 seconds.
5. Release the power button.
6. Reconnect the battery and MagSafe power adapter.
7. Press the power button to turn on the computer.

Resetting the SMC on portables with a battery you should not remove on your ownNote: Portable computers that have a battery you should not remove on your own include MacBook Pro (Early 2009) and later, all models of MacBook Air, and MacBook (Late 2009).

1. Shut down the computer.
2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
4. Release all the keys and the power button at the same time.
5. Press the power button to turn on the computer.
   Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.

Maybe a failing disk.

Hold the Alt(Option) key while restarting: after a while it will display the disks you can boot from: choose the Recovery disk: after that started you choose the Disk Utility and choose the main Disk, do Repair Disk. After that succeeds, restart and make backups backups. Use Disk Utility and see on the bottom of the page if it says "verified" as the S.M.A.R.T. status.