Bear in mind, I didn't read all of those threads start to end, so if I repeat something there please forgive me.
Are on the latest bios version? Sometimes bios upgrades can fix these problems.
Are your bios settings stock? Have you tried doing a reset to safe settings in the bios?
With all due respect, the mobo looks like a very old, low end mobo. It has no support listed for windows 7. (ASUSTeK Computer Inc. - Motherboards- ASUS M2N-MX SE
In my experience, this has either been a driver
conflict or a hardware issue. If hardware it has usually been a hard drive or memory, with the occasional optical drive problem. All the reading I've done through googling your problem today suggests exactly the same.
This is everything I can think of (apart from stuff mentioned above)...
You could try and disconnect your optical drive(s) and see if it boots, if it does the drive is probably faulty.
You can try running memtest to check your memory, if you haven't already.
You could try Hiren's boot CD V14 and run one of the many HD diagnostic or HD Management tools on there. Some of these tools are quite good and will pick up errors chkdsk and windows doesn't find.
The board only has two sata ports, but you could move your hard disk to the other port (if its a sata drive) and see how that goes.
If it's an IDE drive there's not much you can do Check that no two devices are configured as master or slave. Generally though, system won't boot at all if this is the case.
Remove all hardware connections, and reconnect to ensure proper connection. remove and replace memory, video card, sound cards etc.
For your hard disk you can try chkdsk /r to check the integrity of your HDD.
or sfc /scannow to look for OS inconsistencies.
Boot your computer and select last known good configuration
Try a system restore if the problem started after installing updates, drivers
Boot off your Windows CD and going to to recovery console and do a repair install. This could take some time.
Download passmark (http://www.passmark.com)
and run some tests and see if it shows any errors.
If none of this works, you may be looking at a faulty motherboard.