I will give you the normal problems then we can go from there.
You need to ideally use either
FireFox or
Internet Explorer, as others might not be supported by MZ.
You cannot watch games on Google Chrome or Mac PC's for instance.
Check you have the latest versions of Java and Flash Player installed on your computer.
Java http://www.java.com/en/download/inc/windows_upgrade_ie.jsp
Adobe Flash Player http://get.adobe.com/flashplayer/
At present there is also a problem when users have the
Live Scores activated. So if you have anything in live scores please delete them.
Double-check you don't have any firewall or ad blocking software like Kaspersky etc. blocking MZ.
Clear your cache by pressing
ctrl & F5 together on the main MZ screen
And finally, just check, and alter if necessary, the 3D settings to suit your PC to get the best quality possible.
Good luck
John.