The metalized holes are where the motherboard sits on the standoff's & you use screws through the holes to connect the motherboard to the case & ground it. Refer to your motherboard manual.
my case did not come with all the standoffs I needed, I am short 1 so do I need to connect all the metalized holes to make the motherboard work? I know the question sounds stupid but I have gone through 2 Asus M4A89GTD PRO USB3 motherboards because either the video wont work or nothing works. I do not have a standoff or a screw in next to the 24pin connector and no fans including the CPU or the power supply work. I know for a fact that both the CPU and the power supply work because I have troubleshot them on another computer.
1) It is ideal that they are all connected but one missing shouldn't be an issue (had it happen myself once without issues). You could try removing one by front panel connnectors and place by the 24pin connector to see if helps. You could go to a local PC shop and pick up more standoff's to use.
2) As for your build issue, do you have the 8pin ATX plugged in by the CPU? Do you have the front panel installled correctly per the manual? Here are further tips to review & try for troubleshooting: