First, my xbox would have one red light and E 74. Then when I opened it
up and booted it I got three red lights and 0020. I took out the
motherboard, replaced the heatsink compound and did the x-clamp fix,
but I couldn't get nylon washers in the right size so i just used no
washers at all. Varying the tightness of various x-clamp bolts gave me
0020, 0003, 0002, 0001, or it would boot up to the black screen and I'd
get E 74 again. Other times the xbox would almost immediately overheat.
Most of the time I would get 0020, though. At that point, I gave up and
I just tightened up the bolts replacing the x-clamp a certain way
(nothing seemed special about it) and put the motherboard back in the
case without testing it. I screwed everything back together, and since
the heads of the bolts were thicker than they should have been, the
motherboard didn't really sit flat in the metal cage. But i just
screwed the motherboard back into the cage not to tight with the 9
small silver screws, which I would imagine put some stress on the mobo.
Then I pu the rest of the case on and the 6 long screws, and once I had
snapped everything back together I tried booting it up. To my great
surprise it booted up fine! I played some halo 3 and it has booted up
fine every time (3 times) since then
Many people have got this error You need to replace the xclamp and make sure there's
extra pressure (less than half a turn) on the front right corner of the
GPU. You can read more about xclamp replacement here
its not an issue with ur HDD so no worries....
a very helpful rating is appreciated for answering ur query