Same problem when the computer is running a different OS? Use a Live CD/DVD or USB flash drive containing a complete bootable computer operating system (OS). When you boot a computer from it, the OS loads into and runs from memory instead of a hard drive. This allows you to run an OS without installing it or making any changes to a computer's current configuration.

To create one, download an ISO file containing the OS you want to use, (such as Ubuntu, Slax or Zorin), then use something like ISO Recorder to burn it to a CD/DVD or USB key. Now boot your computer from that disc/key and your computer is now running that OS instead of the one on its hard drive.