In bulb mode you need to press the remote to open the shutter and press it again to close the shutter, unless you have mirror up mode enabled where you would press once to raise the mirror and a 2nd press to open the shutter. Bulb mode is not the ideal thing for Star Trails. Use the following as a guide
Lens wide open, or stopped down a little for extra clarity
30 secs exposure
Manual mode and manual focusing
Iso as high as your camera can go before noise gets unacceptable
Lock the release on the remote and let it fire away. Bear in mind that most nikons are limited to a release of 100 frames so you over come this by unlocking and relocking the button if you want longer trails.
Drop all the files into starstax and it will create the trail for you.
Bear in mind that you might not get a 30 sec exposure if you live in an area with bad light pollution.