MacBook Pro freezes

Which version of OS X are you using? when you say it freezes in a grey screen, do you mean after the dock has loaded, or on the boot screen where the Apple logo comes on?

Also, do you have any backups i.e. Time Machine/SuperDuper that you can restore from?

or, have you recently upgraded to Snow Leopard 10.6? or installed any new software?


Have you tried running the Apple Hardware Test?

Apple Hardware Test (AHT) contains a suite of diagnostics that will test the hardware of your computer.  It's is a great way to rule out a hardware issue when troubleshooting your computer.

For Intel-based Apple computers shipping with Mac OS X v10.5.4 or earlier, Apple Hardware Test is located on the Mac OS X Install Disc 1 and should be included with your computer.

For Intel-based Apple computers shipping with Mac OS X v10.5.5 or later, Apple Hardware Test is located on the Applications Install Disc 2 and should be included with your computer.


To start up your computer in Apple Hardware Test:

1) If the computer is already on, insert the appropriate disc into the optical disc drive, then restart. If the computer is not on, turn it on and insert the disc as soon as possible after startup.

2) Press and hold the "D" key before the gray startup screen appears.

3) It takes a minute or so for Apple Hardware Test to start up and inspect your hardware configuration. While this is taking place, an icon appears on the screen:

When the process is complete, select your language and click the right arrow. If you aren't using a mouse, you can use the up and down arrows to select a language and then press the Return key.

4) The Apple Hardware Test console appears. You can choose which sort of test or tests to perform:
To perform all of the basic tests, click the Test button or press the "T" key or the Return key.

To perform a more thorough diagnostic test, select the "Perform extended testing" checkbox under the

Test button before you click the Test button.

Your test results will appear in the window in the bottom-right of the console.

The Hardware Profile tab of AHT provides specific information about your computer. To see this information, click the tab, then select a subject area on the left.

To exit AHT, click Restart or Shut Down at the bottom of the window. Remember that clicking Shut Down will not automatically eject the disc.

http://support.apple.com/kb/HT1509


Hope this might help you a little!

If the previous suggestions do not work:
Unplug your MacBook, take out the battery, and hold the Power button for 10 seconds or so, then put the battery back in, plug in the MacBook, and try to boot up again.

I will try the test when I return to my house, I will let you know the results

Before you do anything else, see if you can safe boot by booting while holding down the shift key. This will force a disk directory rebuild (much like Windows ScanDisk) and will also prevent extensions and programs from loading that might be crashing your computer.

It came up fine in safe boot