I followed the instructions for installing Scapy for Python2.7 (Running Scapy on Windows with Python 2.7) on win64 however the sniff() function doesn't work and ends abruptly. What steps should I take in order to fix this?
Those instructions are very outdated. You should remove both pycap and dnet. They are very old...
The latest dev scapy version (https://github.com/secdev/scapy) is much easier to install. Please follow the latest doc, which is very clear:
http://scapy.readthedocs.io/en/latest/installation.html#windows