It seems the 64bit drivers are the problem. There are quite a few posts regarding this issue. I'd try running the 32 bit drivers even though you've got a 64 bit system.
Be patient, although MyDmx is a powerful program, and (once learned) quite easy to use, it's not the most user friendly application to get started with.
Be sure to search the forum for specific questions on each problem you run into. Most of the answers are here, but it takes a little research to get to the root of the problem.
Here are a few suggestions:
1. unplug the dongle during start-up.
2. plug the dongle in BEFORE starting MyDmx
3. use as many of the profiles in the scan library as you can for your lights.
4. the scan library profile editor is in the MyDmx folder in the start menu. It's highly recommended that you learn to produce your own profiles, but Jingles is an expert advice giver in this area. Be sure to get to know him.
5. test everything! addresses can screw up everything for you if the profile isn't correct.
6. patience and perseverance will pay off greatly.