That's a fairly new laptop so there should be a recovery partition on the hard drive that you access at boot time with one of the Fn keys, often F11. Your Users Manual should tell you how to do this. Much better to do this than depend on a downloaded .iso file which can contain anything, including malware.
I couldn't find an English version of the manual at the ASUS site so can't be more specific than that, sorry.
Edit: If you upgraded to Windows 7 from Vista then please ignore my post.