How to be 100% sure you're not infected?

[WinXPert]

Setting aside firmware infections (e.g. BIOS malware), the "system image" golden rule applies, as other members described above.

If you have a known clean system image, you can use it to restore your system to its exact state, as it was when you created that system image (granted that upon restoring your system, the system partition is wiped, and not "incrementally restored" or similar).

Yes another way to start at a clean slate without reinstalling Windows. And it takes 5-8 minutes. A God-send when HDD crashed or malware testing gone haywire.

i do , you can't load my OS without my password

You can boot mine, but I can roll it back easily

IMO using tools for such things is simply unreliable, just format and re-install the OS.

When repairing customers's PCs, that would be my last option if everything else fails