That's better. The manufacturer name always helps, as does a picture. Yes, that PSU will handle the GTX 960 as long as you don't go OC'ing anything. But you'll have to use a Molex to PCI adapter. Not the best solution, but doable if you can't afford to upgrade the PSU. The GTX 960 may come with the Molex adapter, I can't remember.
No real problem. The GTX 960 4GB should be a balanced GPU for the Athlon 4 core. The PSU is a bit light, however. Link us to the exact model Rosewill 400W so we can check the nameplate specs.
That's better. The manufacturer name always helps, as does a picture. Yes, that PSU will handle the GTX 960 as long as you don't go OC'ing anything. But you'll have to use a Molex to PCI adapter. Not the best solution, but doable if you can't afford to upgrade the PSU. The GTX 960 may come with the Molex adapter, I can't remember.