VM mysteriously became unbootable

[Joymaker]

Configuration:
host: Mac OS 10.9.5
Guest: Windows 7

In January I installed VirtualBox on my Mac and created a standard 25 GB virtual hard drive. I installed Windows 7 (or maybe I downloaded the free VM configuration that Microsoft offers, I can't remember). I was able to start and use this VM several times.

Half a year passed. No upgrades to the OS, and none to VirtualBox that I can recall. I came back to the project, started up, and promptly got the error message "Fatal: no bootable medium found! System Halted”. So I went into Time Machine and restored the virtual hard drive from its earliest backup, less than two weeks after creation. After fighting long and hard with Virtual Media Manager, I got VirtualBox to accept this hard drive in place of the other, and started again… With exactly the same results. Which leads me to wonder if something is going on with the VirtualBox software, rather than the media file.

I’m looking for help on diagnosing the problem. Anything less laborious than the 6 or 7 hours it would take me to rebuild that VM from scratch, would be much appreciated!

Configuration:
host: Mac OS 10.9.5
Guest: Windows 7

[mpack]

I'm afraid that "mysterious" is how such questions will remain, until you get in the habit of providing adequate diagnostic data.

A log file is a good start: right click the VM in the GUI, select "Show Log" and attach the saved and zipped "VBox.log" here.

[socratis]

I would also like to know how this ties to "Update now exits without error message (#16841)", where you claim that you can't even start VirtualBox. So, what's going on? You were able to start VirtualBox after all and then you were not able to start the VM?

Common denominator: have you checked your hard disk lately?