BTX is not compatible with ATX cases. Even if the screw holes line up properly the placement of the i/o panel in the back of the system is different and will not match up to an ATX case. Basically the i/o panel is on the bottom with BTX as opposed to being on the top in ATX.
Another thing is the official BTX standard was dropped from further development in 2006, so any system built with a BTX-like form factor is a mutation from the BTX standard to a proprietary form factor after official development was dropped.
Even if your board is not a true BTX board, which it looks to me like it is not, it is still a Dell proprietary board and will likely not fit in any case except the one it came in.
8 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
Logitech X540 5.1 Surround
2X Acer 23" LED - Eyefinity: 3840x1080
Microsoft Sidewinder x4 KB
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