The 'boot override'? I'm not familiar with this term but basically you need to change the 'Boot order' so that the USB is first.boot override so that it boots the USB drive instead of the OS
Yes.For the disk, which memtest do I need to use ?
The "Pre-Compiled Bootable ISO (.zip)" ?
We already did..Hmm, just a thought and I don't want to interfere, but with all those bad sectors and hardware related crashes it won't be a bad idea to run seatools and check your disks....
Yup that's bad memory alright. It's possible the resulting bsod's caused the corruption on the HDD but in any case you'll need to change that RAM. How many sticks are you running?I think that it is a memory problem.