Actually I had an issue like that on a board, worked fine in a different case, would post once the FP connections were plugged into my cosmos case.  Case was free so I couldn't really complain there.... but it did not turn on, and once unplugged I had to reset the BIOS before it would post.  Tried it again later same issue.  So I found you can have this issue form a hosed front panel if your cases front panel controls uses a circuit board for everything it may be bad causing this issue.