windows - Laptop sometimes freezes when I open websites requiring excessive memory / CPU usage

I've installed Chrome on my laptop (Windows 7 as prime OS, 4GB RAM and a Core i5 processor).

Sometimes when I open certain websites that require more memory and CPU usage, my laptop freezes, and the only way to shut it down is to hold the power off button for 4-5 seconds.

What could be the root cause, and how can I fix it?