I don't work for VHX but just trying to help. Looks like the system logs people in using a key that's generated by the link(s) in your email, so if you're having trouble viewing the video(s) first try go to the email you signed up with and access the site through one of those links. Looks like you'll have to come through a link through the email if you want to see anything.
If you come onto the purchase bundle page (all Pink Banners/says 'Get Carmilla Movie' at the top) at the very, very bottom of the page on the left hand side there is something that says 'Watch'. As long as you've gone through and accessed the site at some point via email you should be able to log in to the video viewer by clicking that text at the bottom.
And if you're still looking for things to try I would recommend opening up a different browser or a Incognito/ Private browsing window and trying to go through the same steps mentioned above. Browser history and cookies/cache can be tricky so that could be causing issues for some people. Also try a different device, eg. accessing it on your phone vs. accessing it on the computer.