If you don't mind opening up your system the easiest way is to hook it up as a second drive on the system that does work. Then GDB will work much faster. GDB works best when it is installed on a working system and the drive in question is a second drive.
Also it may be worth waiting to see if Paul Komski happens upon this thread. He is very knowledgeable about these things and it may be a simple matter of undeleting the partition. Again it all depends on what they did to get rid of the OS.
On another note, once you recover your files and if these two systems are identical you should be able to clone your existing drive onto the empty drive and make it work just fine with the other system, if you so desire.
8.1 Pro 64bit
AMD FX 8350
Asus Sabertooth 990FX R2.0
24GB GSkill/Corsair 1866MHz
2x XFX 6870 1GB
SSD - OCZ V4 128GB/Kingston 120GB
HDD - 3TB/2x 750GB/500GB/250GB
Cooler Master HAF 932 Red
CM Hyper 212 EVO w/2x SickleFlow 120mm Red
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Microsoft Sidewinder x4 KB
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them."
- Albert Einstein