Windows 7 - Please select boot path or insert bootable media

Windows 7
Gateway GT5676
Dual Internal 300GB hard drives (One empty, One Windows 7 OS and assorted files)

What the hell! I went to start my pc this morning and I get a black screen with a message similar to :"Please select boot path or insert bootable media".

This went on thought several restarts, I tried to "F-10" and check the boot sequence to make sure something wasn't fouled up there, but I couldn't get in.

Finally thinking something was corrupt in the boot registry, I mounted a backup image using "Macrium". This all went fine, but when macrium restarted (for a file check) the same message appeared again.
Thinking I must have a bad hard drive, the only thing I could think of to do was to was to switch wiring to with the additional hard drive, mount the backup immage on it and see what happened.
After switching both power and sata leads, I fired her up, and everything was fine, macrium went through it's file check and the pc booted normally.

This is throwing me, because I thought I would have to change the boot sequence and now I am confused as to what my problem was before? could it be bad power or sata leads? and will the pc check all hard drives for a OS, then when a OS is found go ahead and boot?
Thanks for any help in this mystery.
N2

This may sound dumb, but can you tell which hard drice you are booted into? I ask because, if the boot sequence in bios is 1st HDD #1 and second HDD #2, if it can't boot into #1 it will boot into #2. Whichever disk you are booted into will always be C drive in explorer. Try going to disk management and see which drive it is. I would go to the hdd's manufacturers site and download the diagnostic test for both drives. That will eliminate that problem. Or it could be as you mentioned, a bad sata cable. Change the cables back and see if the situation happens again.

I have had strange problems in the past related to SATA connectors getting corroded or not making tight contact with the mobo or HD. It's similar to clearing up static on your phone by unplugging & re-plugging a modular telephone cord/jack.

SATA is great compared to the slower IDE technology, but the IDE cables never gave me any problems because the connectors were much more snug.