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I have two Dell Inspirons; one is a Windows 7 machine, the other a Windows 8 machine.

Knoppix 7.4.2 LiveDVDs and LiveUSBs will boot and run on both of these machines
if built-in boot choices are properly made.
For both machines, one must select the boot device order to select DVD or USB
to boot first, before other available, bootable devices.

My Windows 7 machine does not have either Secure Boot mode or UEFI boot options;
its only boot choice is 'BIOS'. All recent Knoppix versions handle this mode.

For my Windows 8 machine, to use Knoppix 7.4.2, one must de-select Secure Boot mode as a boot option;
Knoppix 7.4.2 doesn't handle this mode. For this machine one has a choice of either
'BIOS' or UEFI. Knoppix 7.4.2 handles both these choices without Secure Boot.

If Secure Boot mode is selected, Knoppix 7.4.2 booting support must be revised
to allow this. An earlier post in this thread speaks of success in the revision
using some supporing files from recent versions of Ubuntu.

One needs to get familiar with one's own machine to determine what its boot
choices are. Your machine may differ from my Inspirons. If you haven't already,
locate and get familiar with the user manual for your machine.