Trend Micro Rescue Disk is a free tool that will let you use a CD, DVD, or USB drive to examine your Windows computer without launching the operating system. It can find and remove persistent malware and security threats that may be present on your computer. It can scan hidden files, system drivers, and the Master Boot Record (MBR) as well.

More details on its home page.

Also see:

  1. Free Bootable AntiVirus Rescue CDs
  2. Five Best System Rescue Disks.