Possible shorting between Motherboard and case

[Majorai]

I decided to change my case from a Nanoxia Deep Silence 1, to a Corsair 500r. However, when I attempted to start the computer the leds and fans start for a fraction of a second, then any subsequent attempts produce nothing. I have made sure I am connecting the front panel correctly.
If I put all the components into my testbed, the computer boots up and works with no issues.

I'm convinced that the mobo is shorting on the top 3 mounting holes on the 500r (they're not traditional screw-in stand-offs). It may be that I am missing something incredibly obvious, but I can't for the life of my figure out what it is.

Any further tests I can try would be greatly appreciated, or is it time to just send back the case and get my second choice?

Specs are:

i5 4690k
MSI z97-G45 Gaming Mobo
16GB RAM
MSI GTX 980 4G
Corsair RM850x PSU

 

[clutchc]

Yes, that would be the first thing to check. See if you have an extra standoff installed where one does not need to be. It may be pressing against the back of the circuit board. Another issue I've seen (and done), is one of the IO plate's bendable tabs ends up sticking into one of the rear ports, generally a USB port.
If the board won't run while in the case, chances are it isn't the case's fault. Generally it is user error.
You may also want to check that none of the PSU cables are frayed or have an errant strand of wire poking out from a connector.

 

[Majorai]

Thanks for the reply clutchc, turned out that the centre stand off supplied with the case was slightly different, I just needed to remove it and swap it to one of the spare standoffs.