Your power supply is the thing on the top left where all the cables are coming from.
You can find all we need to know about you powersupply on its side.There should be a power destribution table like the one on this power supply.http://www.hardwaresecrets.com/fullimage.php?image=42969
If your power supply has more than 30A combined power of all 12V rails.Or it may be just one rail like on most power supplies.Than its good enough for a GTX 670.If on the other hand it has less than that... well you better buy a new one.
I highly recommend this onehttp://www.newegg.com/Product/Product.aspx?Item=N82E16817116014
Its priced very well and has all the power you will need now or in the future.