Too late now of course, but there would have been a Windows utility on your laptop (ASUS utility) which you could have used to make a set of factory recovery discs as a rescue plan in the event of hard drive failure.
As it is, you'll have to contact ASUS to see if they can send you a set.
Failing that, you'll have to buy Windows 7, install it, then download drivers for your specific laptop model from the ASUS website, if necessary using another computer which has internet access so you can download the network drivers initially.