I have Windows Vista + CKII (patch 1.05d) and I had the same problem.
The login button didn't do anything, the only way out was hitting it so often until Windows tells me that the program has stopped working.
Problem was my inpatience....
When hitting the Login button once, I had to wait for some time (more than 5 seconds) for a reaction.
Not saying that you do the same mistake that I did, but maybe worth a try...
Good luck,
Roland