Wattage is almost irrelevant these days and companies such as AMD only make recommendations in it because many of their customers wouldn't understand what to look for in PSUs. Regardless, that PSU is almost definitely too weak for that card. It doesn't seem to be able to handle enough +12V amperage.
I suggest getting a Radeon 7750 instead of the 6670. It's a little more expensive, but it's much faster and uses much less power. It has a beter chance of working with that PSU. If you want to be sure, check the PSU's label for how much +12V amperage it is rated for.