I don't mean to pull people from this site because this site is very very helpful but there is a HUGE database of RROD Repair and diagnosis information that would take months even years to accumulate here. The Xbox Experts Site even has a step by step guide to diagnose your xbox and then a list of possible fixes.. I have repaired over 50 xbox's with this and had great results.
What you see in step 39 are not washers. Just screws with large flat heads. You need flat washers. Usually they are labeled 5mm because of their inner diameter. they should be 1mm thick and the outer diameter should be about 8-9mm. They come in packs of either 4 or 10 depending on if you go to Lowes or Home Depot. I think Lowes is the one that sells by 10.
The laser is most likely the cause of your issues. So you have three options. 1> Tweak the laser to make it stronger, it will eventually die but this is the cheapest, fastest fix. PDF Link (Difficulty: Hard) 2> Replace the laser. (Difficulty: Low to Medium) 3> Replace the DVD drive. (Difficulty: Physically easy. The software can be hard to very hard) To replace the whole drive you need to extract the key from the dead drive and spoof it onto the new drive. All of these will void your warranty.
This is a bad solder joint under either the HANA chip or the GPU itself. Essentially the same as RROD except because it's not showing the RROD Microsoft wont repair it for free... The xbox need's a professional reflow. DO NOT, UNDER ANY CIRCUMSTANCES try the towel trick or penny fix. BOTH will make your xbox a very expensive doorstop. There is the RARE occasion that this is a bad solder joint under the connector where you plug in the av cables. Either way the xbox needs to be Reflowed. A great resource for this is Xbox-experts.com. Good luck!
[EDIT] You can now aquire the CPU and DVD Key with what is called the Reset Glitch Hack (RGH) Only the very newest slims and the xenon are not RGH'able Google "reset glitch hack xbox 360" For more info. [Original Message] Your xbox needs to be JTAG-able. And chances are high that it is not. The only way to get the key without the original drive it by JTAG. If you xbox is running the "Blades" Dashboard its a pretty good bet you can JTAG. If you are running the NXE dashboard its a safe bet you have a very expensive paperweight/door stop/dvd player at least until they discover a way to JTAG after the update, if they ever do..
Jack Cracker is correct however you do not need to used the hacked firmware if you don't want to. You can use the stock firmware from the good drive and just spoof it as the dead drive revision with the dead drive's key. To do this you would also need to read the working drive to get the stock firmware. For example. (very much dumbed down! read the PDF previously mentioned by Jack) If you had a dead Samsung and a working Benq. -Read both drives and save the original firmwares. -In jungle flasher firmware tab use the Benq stock firmware as the target and the samsung stock firmware as the source (you will understand once you explore Jungleflasher a bit) -Make sure you spoof source to target. The should essentially flash the benq with the Samsung key and spoof it as a samsung so the xbox thinks it's the same drive. -write and you should be good.
It's quite possible that someone did a 12v fan mod to this xbox and Microsoft didn't take the time or just didn't care enough to look at it (I have even heard of people sending modded systems in for repair and getting repaired xbox's back no questions asked). There are many methods to do the 12v mod and some are quite obvious.. some not so. It may just be as simple as de-solding a wire or two.. But it may also be as complicated as replacing mosfets (if they went bad and were bypassed in a cheap fix repair). If the xbox is out of warranty just take it apart and take a close look for out of the ordinary stuff (ELECTRICAL TAPE IS NOT NORMAL!). If it's in warranty call Microsoft see what they say to do. Be sure to stress it came back from the repair this way!