Double check that the standoffs are properly installed for each motherboard mounting hole.
You may want to do a bench test: http://www.techsupportforum.com/forums/f15/how-to-bench-test-your-system-262998.html
You may want to do a bench test: http://www.techsupportforum.com/forums/f15/how-to-bench-test-your-system-262998.html