My Ubuntu workstation froze completely, so I had to reset it.
Afterwards, when I launch VirtualBox (v 4.1.4) and try to power on a Windows 7 image, I just get "FATAL: No bootable medium found!".
Note: I did have a working Windows 7 installation in this image that I've been using for the last 10 months. So this is not the same situation as when creating a new virtual machine.

I've tried resetting and powering off the virtual machine a couple of times, but no luck.
Is there any way to rescue / continue using this Windows image? Or is the only option starting over with a new Windows 7 installation? I hadn't saved any snapshots.
In my VirtualBox VMs/Windows7 directory, I still have the 28 gig .vdi file:
$ ll -h
total 28G
drwxr-xr-x 4 jonik jonik 4.0K 2012-02-08 14:27 ./
drwxr-xr-x 3 jonik jonik 4.0K 2011-05-18 19:02 ../
drwxr-xr-x 2 jonik jonik 4.0K 2012-02-08 14:25 Logs/
drwxr-xr-x 2 jonik jonik 4.0K 2012-02-08 14:25 Snapshots/
-rw------- 1 jonik jonik 13K 2012-02-08 14:27 Windows7.vbox
-rw------- 1 jonik jonik 13K 2012-02-08 14:25 Windows7.vbox-prev
-rw------- 1 jonik jonik 28G 2012-02-08 14:27 Windows7.vdi