I have to, at least partially, agree with above...
Here's my story (sorta summarized)
Accidentally left cabinet door closed while playing few hour session. Said "OH SHIT!" when I noticed and opened the door to my 360+ degree 360.
Turned it off and actually didn't play for a couple days.
Next time I go to play, video is kinda wonky... turn it off and back on, video is fixed.
Next day I turn on the 360, seems to boot fine but no video or audio... and no RLoD... Tried different cables, no different.
Learn about XClamp, pennies, eraser, towels and all that shit... Decide I'm going to try some out as my Box no longer qualifies for warranty.
Spend 1/2 day trying to implement XClamp fix. (After booting the first time after doing so I start getting the 3RLoD) AND every time I make an adjustment I get a different error code.
Codes I received at various points: 0001, 0002, 0012, 0020, 0022, 0102, and even 1022!!
The most common I ran into were: 0020 (the ?? one), 0001 (PSU error) and 0102.
Modifying the amount of tension on the screws and heating the board/CPU/GPU would trigger these issues.
I've now gotten my 360 going twice by readjusting the HS screws and heating it up with a heat gun.
I just finished doing it the second time, I'll report back once I see how long this lasts.
I think that tightening your screws too hard will trigger 0020 (and even 0001) which warps the board, similarily how the XClamps did. So when doing XClamp fix, be sure to start with the screws barely even snug and keep trying to boot. AND remember to boot it up twice for each test so that you're sure the error has been cleared in the POST.