Almost all laptops come with a way to make your disks. Since you don't list which make or model laptop you have then all I can do is refer you to the owners manual, which might be on the harddrive too. At minimum you can make a System repair disk from windows Backup & Restore utility; and if you have an external hdd you can create an image file of your drive exactly as it is now plus run a backup.
As for the slowdown it could be a number of things; heat buildup, hdd full or problematic, laptop put into power saving mode by someone else (software), malware/virus ...
The important thing here is to have your disks so you dont end up buying windows again, and to backup your important files (because its only a matter of when will your hdd break, not if it will)