New MacBook Pro will not power up!!

Just received MacBook Pro Unibody for Christmas. New to Mac. Would not load excel document yesterday, decided to restart from power button. It shut down, came back on for a few seconds to gray screen, apple and spinning wheel, then turned black. Waited for a bit to start up, nothing. Pressed power button, up came grey screen, apple and spinning wheel then black screen. This took just a few seconds. Repeatedly tried to power up and the same thing happens. Any ideas, please!!

It's generally a bad idea to forcibly power down any modern computer before you take appropriate steps to make sure there's no disk activity. If you experience a lock-up condition, you want to use Command+Option+Esc to bring up the "Force Quit" dialog and end the offending application.

As you've experienced, forcibly powering down the machine can create corruption in the filesystem that can keep the machine from booting. The next step is going to be running Disk Utility from the Recovery partition. To do this, start with the machine turned off. Turn it back on and immediately press and hold Command+R. Continue holding until the Recovery options window appears. From there, run Disk Utility, select your Macintosh HD volume in the left window pane. Then, click the First Aid tab. Run Verify/Repair Disk and Verify/Repair Permissions.

When finished, close Disk Utility and restart the machine. It should be OK. If it isn't, you may have a more severe problem. Post back with your results.

This article has more information about Mac OS X Lion Recovery options:

OS X Lion: About Lion Recovery