The bracket shouldn't be causing a short, unless it's shorting on the motherboard already.
To me it sounds like a bad PSU. But what i'd suggest you do first is breadboard the computer outside the case on some cardboard, or other none conductive material. That should eliminate the possibility of the case shorting out your computer.
If the problem persists i'd blame the PSU. I had a similar issue not that long ago, and it was my PSU.
PS: Because this post is potentially related to a PSU issue i'd like to inform any potential readers of my recent experiences with Silverstone. I'd like to apologize in advance for potentially hi-jacking the OP's thread. You do not have to reply to this part of my message. All i ask is you read and take note.
SHORT: Stay clear, don't waste you time or money.
LONG: I've already returned one PSU, the Decathlon 750 once already without much trouble at all. Other then the fact i got smacked with the brokerage fee on the new unit they sent me. Silverstone seems to think they're above the consumer, and they don't care about there customer service. They didn't even take the time to punctuate or capitalize any of their e-mails. Needless to say, the replacement unit was also bunk. And they're refusing to cover shipping or brokerage, just shipping one way. In my mind this is total crap, i've already spent $120 troubleshooting their junk. Might i add, over a month of computer downtime, had my mobo replaced as part of troubleshooting the second PSU, and countless hours pulling my hair out. My advice to the Tomshardware community is to remove Silverstone thoughts altogether. Save yourself a potential, recurring, headache.