Stock GB ROM for i896 is Rogers KH2, not AT&T KK4. Rogers one-click Odin packages are available in Development section. I'm not sure Rogers and AT&T bootloaders are exactly the same. I'm assuming you flashed AT&T KK4 ROM without bootloaders so you have Rogers bootloaders with AT&T ROM and this is probably causing the problem.
Try this first: remove the battery, remove both SIM and SD card (if you have one), insert back the battery, hold both volume keys, connect the USB cable to the computer. See Download mode now? If not, get or make a jig, force the phone into Download mode, flash Rogers KH2 one-click ROM and see if the phone loads the system correctly.
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- Samsung i896 Captivate, 16GB int, 16GB ext, CM 11 Android 4.4.1 (backup phone)