I had this exact problem trying to re-texture a free 3DS model I'd downloaded last week.  Did some research, and it appeared that the normals in the original model might have been facing the wrong way i.e. backwards, as the texture which I thought I'd applied appeared on the back of the model, and was thus invisible from the front.  I'm no expert, so shoot me down if you want, but it might help.

My self-build system - Vista 64 on a Kingston 240GB SSD, Asus P5Q Pro MB, Quad 6600 CPU, 8 Gb Geil Black Dragon Ram, CoolerMaster HAF932 full tower chassis, EVGA Geforce GTX 750Ti Superclocked 2 Gb, Coolermaster V8 CPU aircooler, Enermax 600W Modular PSU, 240Gb SSD, 2Tb HDD storage, 28" LCD monitor, and more red LEDs than a grown man really needs.....I built it in 2008 and can't afford a new one, yet.....!

My Software - Poser Pro 2012, Photoshop, Bryce 6 and Borderlands......"Catch a  r--i---d-----e-----!"