Why are my photos white when I do a long-exposure?

The problem is that you have too much light entering your camera so your photo is becoming over-exposed. To solve this you need to let less light in, and there are five ways you can do this:

1. Stop down your aperture (if possible)
2. Reduce your shutter speed
3. Lower your ISO (if possible)
4. Put a filter over your lens (ND or CPL)
5. Wait for the ambient light levels to drop, like during dusk or dawn