I wonder if the card is fully seated in the slot?
If so, it sounds like a short may have occurred either in the MoBo or 450, hopefully the 450. I would return/exchange the card (assuming you have time left) and install the replacement, see if the behavior persists. You have more than enough power for the card, assuming your MoBo driver is up to date as acdcfanbill asks, it has to be a hardware issue.
What does your event log have to say about things?