Need Knoppix Guru to Help Debug Hardware Problem

So here's the situation. My friend was having trouble with his PC. It was BSOD-ing and rebooting randomly. Eventually, his system became corrupt (seemingly irrepairable), and we decided it would be best to erase the disk, reformat and reinstall.

However, the problem had gotten worse by that point, and reinstallation became impossible (the system either hangs or reboots part way through). I'm thinking, it's a hardware fault for sure. So, I've run diagnostics on every part, nothing. Then, I replaced nearly EVERY component (PSU, RAM, HD, DVD, Motherboard GPU...everything except the CPU) with ones I know to be in good condition, AND IT HAS THE SAME PROBLEM.

So...it has to be the CPU, right? To me, this doesn't make a lot of sense, and I decided to try one last thing, Knoppix. I remember having been able to boot Knoppix on his system earlier on in the game, and if the CPU is bad, I shouldn't be able to do so.

When I attempt to boot Knoppix regularly, it fails (freezes). However, when I boot in debug mode, IT WORKS. That is to say, it boots, and no matter what I do, it won't run into any errors or reboot itself. The CPU must be okay, right?

So...my question is WHAT THE <Insert Page of Explitives Here> IS GOING ON? It looks like this PC can do nothing but boot Knoppix in debug mode.

Does anyone know what Knoppix does differently in booting from debug mode? Knowing this is key to debugging this problem. Also, how can I view the info/messages Knoppix prints to the screen while booting? This happens too fast for me to read while the system is booting. Is there a way to go back to it?

Thanks.

To see what's gone flying by, type: dmesg|more from a shell. You might also give more info as to the hardware specifics, the output from: lspci -v, again from a shell might help.

you wouldn't normally think of the cpu as faulty ....
but I have seen it happen.

also, have you re-burnt your knoppix CD
it may be faulty too

I had a 2nd hand system that booted 'fine' after i changed the mobo
updated the hardware in registry fine ....
but then, later, it wouldn't find the hdd
took an age before i realised the PSU must have been subtly faulty
as the mobo powered on ok
and the cd-roms were found ok
but not the hdd

knoppix in debug mode
would probably be the same as windows in safe mode
you can get it to work as long as you don't use a part of the system that requires the use of the part of your cpu that is faulty