Before you suggest a new graphics card, (Or any component) make sure that the OP has sufficient a wattage PSU from a good brand, if they don't, and you suggest, say a GTX 670 when the person has a generic PSU. Than there GPU or any component WILL break in the future.
To add on to this, to check what wattage is needed for a particular card:
Go to this page: http://www.nvidia.com/object/geforce_family.html, click the card and on the left-hand side you should see 'Specifications'. Click it, scroll down and you will see the power requirement.
Go here: http://www.amd.com/us/products/desktop/graphics/Pages/desktop-graphics.aspx, select which generation GPU it is, select the card and in 'System Requirements' you will see the power requirement.
Also if you want a PSU Wattage calculator, here's one: http://support.asus.com/powersupply.aspx