Go into Catalyst Control Center and check temps. See if you can manually set the fan speed higher. If you can't, it may be defective. How old is the card? If it is still in the warranty period, you can contact the manufacturer for warranty repair or replacement.
If you can set the fan speed higher, set it at perhaps 60% or so.
You could use a program like MSI's Afterburner (free, and your card doesn't have to be from MSI) to set a fan speed profile, so instead of one rate (e.g. 60% as above), the fan will vary based on temperature or load.