How would I RMA my MSI Card?

You would need to contact the support department of the manufacturer. This is unlikely to be AMD who simply provide the reference design, it will be on the box or failing that your supplier.

You need to contact the place where you purchased it from as it is they that will give you an RMA (Return Merchandise Authorization) code.

Bought a 2012 release gpu card in 2015?
http://www.game-debate.com/...0HD%207870
Return procedures vary by country.
You can contact the store where purchased as valid in the UK at least. You can look up MSI wab site support for your country and contact them.
Have a good 500W Power supply with 2x6pins needed to feed the card?
That often causes issues to have a bad brand or insufficient 12V power.

Most likely you will not be able to RMA that particular video card. MSI covers the original owner of the card for three years after purchase. Seeing as how you just bought that card a few months ago, I doubt that it was brand-new.

http://us.msi.com/page/warranty