Q:

Disk Boot Failure - Insert System Disk and Press Enter

Question:
How can a running system suddenly reboot and show the message:
Disk Boot Failure - Insert System Disk and Press Enter instead of booting the OS?
It doesn't seem to be caused by a defective physical disk. Can the disk controller cause it? How can I prevent this happening again?
Details: 

This time, the computer was running Win7 and was always on. Automatic updates are disabled; the computer should never reboot by itself unless there's a power outage, which there wasn't. (Brownouts don't occur where I live.) There are no USB devices attached.
I came home and found that the machine had apparently rebooted and was showing the message:
Disk Boot Failure - Insert System Disk and Press Enter instead of booting the OS.
I had this exact situation once before -- on the same machine but running WinVista -- and a simple chkdsk solved the problem. But on Win7 that trick does not work. I can't access the event log because it doesn't boot. The Samsung 1TB hard-disk itself is only a few months old. I have not tried Tune HD.
I tried booting from the Win7 installation DVD and repair the installation, but the DVD kept hanging during boot. Something was preventing setup from starting, and booting the DVD in safe mode showed that it hung during or after loading the disk driver.
The same disk  wouldn't boot in another computer either, same message.
I installed Win7 on a new physical disk -- that worked. After letting the machine run for a few hours (nothing installed, just a totally clean Win7 without any updates), I came back to the machine and it again showed that message! On a new disk!
I'm beginning to suspect that it's not related to the physical disk, and not to any installed software either. I don't like to install again and then sit for hours and watch the screen, just to try to discover why/how/when this happens. I'm now not sure what to do, what to fix. 

I don't want to install Win7 over and over again, and I need this computer up and running as soon as possible. I don't want to have to replace components one by one either until it's a new machine next to a drawer full of junk...
Can this error be caused by a malfunction in the disk controller, or perhaps in the power supply? I don't have any spare components lying around that I could test.
Update:
One month has passed and the machine has worked fine. Now, it just happened again, the system disk won't boot. Luckily I've now learned to keep important stuff on secondary drives, so I'm just going to format and re-image the system disk and see if it helps. And I'll install a new disk controller at the same time, to make sure the onboard controller won't crash the new image as well. This is getting tiresome.

A:

it can be a fault on the connector the hard drive is plugged into. Which is a motherboard fault..
you could try plugging the hard drive into another connector.
Windows version has nothing to do with this.
you could try a new hard drive.
(I had a situation like that with a computer, new hard drive helped for a bit but then same problem - +that solution didn't last long. proving not the hard drive.  I then tried moving the hard drive to another connector, then was fine for maybe even a year, but then same thing happened with that other connector. Was ultimately a motherboard fault of course.. and it just delayed the problem.. ultimate solution was new motherboard)
Another temporary fix with that thing was booting to recovery consule and doing those 3.. FIXMBR, FIXBOOT, BOOTCFG /rebuild.   Was probably FIXMBR that did the temp fix. though didn't go to what caused the corruption.
There are viruses that can write to the boot record, so in theory it could be that., and resetting the MBR could help..
obviously with any movement of the hard drive to another connector(and that may indeed fix it for a good time or "permanently"), you obviously may have to change a setting in the BIOS to get it to boot from that one. (i'm not sayin you haven't.. just saying if you will move the hard drive to another connector as a solution, then, bear that in mind)
added-Try changing to another controller/  mbrd hdd connector..and then doing a repair installation. (to fix any corruption of the windows installation) also, maybe it may help to do fixmbr fixboot .. from recovery console prior to repair installation.
You can try skipping the repair installation if you want to save time. 
The method is this

Changing to another controller is the most important thing.
Making sure the windows installation that is no longer  corrupt and won't start, (incase eg damaced by the bad controller), and making sure the boot record is fine and the partition active. If you want quick methods, then those mentioned.. (just repair installation if you did it, is a bit slow and may require some reinstalls.. chkdsk can be a bit slow(but obviously use the right switch so it fixes errors).. fixmbr, fixboor,.. are quick).
note- chkdsk is only one thing and as you say didn't manage it.. but it is always something to try , and as you say, it worked once. It can fix some corruption sometimes. important that you use the fix switch or better, in windows itself, that's /R. In the recovery console the options may be less, and there's a /P. but do /? so you see what options there are. and chkdsk is only one thing..   

