If you are using the key off the side of the laptop, that is your license you paid for.
MS insists you get one.
You are entitled to use that to reinstall clean - that is why it is there.
Unfortunately, some oem's insist on you ringing them to activate after using it.
They can't refuse - that is your license . It is a pain to have to do that.
[ A lot of people can't be bothered with that , so they backup the key and oem cert off the HD , install clean without entering the key, then put the key and cert back on. You need to stop and start services to do it that way, so you have to know what you are doing of course. ]
Might be a good idea to make an image of your current system first - you may want to fish some files/folders out after that you don't think you want just now.
There is a built in windows 7 system image app. , but it has serious limitations.
I would d/l the free macrium - it is vastly better - it is also massively quicker. Macrium Reflect FREE Edition - Information and download
I recommend everybody makes an image of their system regularly - the most important thing you can have is a backup image.