I've run into a problem that applies to all Hewlett-Packard computers. Perhaps others, though I have no information about other brands.

On all H-P machines, the motherboard is "tattooed." This means it includes a code describing the machine's original hardware configuration. The tatto becomes important if, and only if, you need do a System Recovery. (A System Recovery - not the same as a System Restore - is the procedure by which you recover the original software configuration of a computer from Recovery Disks, which may be needed if there's been irremediable trouble with your software.)

On an H-P machine, if you make any change to your computer's hardware - add memory, add a drive, etc. - you will lose the ability to do a System Recovery. This is because the tattoo no longer matches the hardware. There are only two ways to deal with this: hire a licensed H-P technician (techs must pay several thousand dollars a year to maintain their license) to obtain a new tattoo from H-P and copy it onto your motherboard; buy wholly new software, starting with the Operating System, and install it on your computer. Either way, lots of money and lots of time and trouble.

H-P doesn't tell anyone about this. I found out the hard way. So this is an alert to anyone with H-P.

I have an hp pavilion notebook.

What you say is right, but if you have to recovery the pc after hardware modification you need substantially the operative system(you can easily download it from p2p and use the license code for the activation) and the hardware's drivers(you can free download them from hp website).

You don't need to pay a lot of money for licenses.

Get the windows copy is maybe the more difficult part, but the best thing to do in my hopinion is send to hell Gates and his traps(expecially windows vista) and install a free operative system based on gnu/linux kernel, like Ubuntu, Xubuntu etc. They are much better than Windows and you haven't to pay nothing for them.