Create an Image of your HDD on an external HDD using a program like Acronis http://www.acronis.com/homecomputing/products/trueimage/index.html then replace the HDD in your laptop, finally copy the image back to your new HDD and all should be well. (Depending on make and quality, HDD have guarantees between 2 & 5 years, and its best to change them when they reach 2/3 of the life expectancy.

Windows may require re-activating after the change, however this is a simple case of following the on-screen instructions and explaining what’s happened.

Hope this helps

Bill