I just got a new Windows 8 laptop and it froze three times today. I was forced to turn it off and turn it back on. What is causing this?

Method 1: Run System Maintenance troubleshooter to diagnose the exact issue.

Follow the steps mentioned below.
a. Press “Windows key + W”.
b. Type “Troubleshooter” without quotes in the Search box and hit enter.
c. Select “System and Security”.
d. Select “System Maintenance” under System options.
e. Follow the on-screen instructions to run the troubleshooter.

Method 2: Follow the steps from this Microsoft KB article and check:

Windows hangs or freezes (Also applicable for Windows 8.1)

http://support.microsoft.com/kb/2681286/en-us

Antivirus Disclaimer : Any data files that are infected may only be cleaned by deleting the file entirely, which means there is a potential for data loss.

Also refer this article: http://windows.microsoft.com/en-US/windows-8/improve-pc-performance