Linux Mint 13. Trouble booting. Can't use installation DVDs.

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http://www.linuxquestions.org – For a couple of weeks my Mint 13 has been turning itself off after booting up. I had to switch off power at the wall before I could re-boot. Now it boots sometimes and sometimes not. I may get a screen with options about recovery mode and memory test etc. but they don't seem to do anything. Then sometimes the first option does work. I tried different distro installation disks (Mint 15, Ubuntu10.04) but I can't boot them from the desktop. When I click the icon it just shows the different folders on the disk. I looked at [URL="http://www.ehow.com/how_6116125_fix-linux-file-system.html" (HowTos)