I just added a self signed SSL certificate on one of my virtual hosts. I'm using Ubuntu Server and Webmin, if that helps. The site I added the certificate for works perfectly, but trying to access a different virtual server takes you to the default server page(var/www). If I type in the url for the other virtual servers with https in front, I get redirected to the site that I added the certificate to. Does this have anything to do with ports? Any advice would be appreciated.
Assuming your server only has one IP address for all the virtual hosts then this behaviour is normal. All traffic using https will be directed to port 443. There can only be one virtual host on port 443 per IP address so this becomes the default one.
As to why your other non https virtual hosts have stopped working we will need more info. As Shane has commented