Built in flash still popping up on my nikon d3100 even if an external flash in?

Ok I got the Neewer tt560 flash for my camera. It was said to work with it find. But when I have it on Program it will flash, but the camera doesn't know it i guess cause it still puts it on a 2 to 3 second shutter speed. And then if I put it on portrait mode, the built in flash pops up. Also the flash works in M mode. But won't work in S1 or S2 mode. Is it broke? Or what? Others said it worked freat with the d3100. But I don't get it. It's not syncing with the camera I guess? If it will work, how do i get it to sync?

Added (1). What flash will work then? Other than the Nikon ones? I don't have the money to get something that cost that much.

I would say it's not the flash or the camera but you. If you're running the camera on full auto that could be the problem. Get off full auto.

There are scene or automatic modes in which the camera will automatically pop-up its flash. However, with a TTL-compatible flash like the Nikon SB models installed and turned on, the camera should know its there and leave the built-in flash down. If the external flash is not TTL-compatible the camera behaves as if it is not there, although it can make it flash in manual mode.

It sounds like that isn't a ttl flash…

You'll have to use the manual exposure setting (M) on your 5100.

When using the flash, you can use any shutter speed 1/200 of a sec or slower.