How to set up VNC connection?

[spleencheese]

Hi there. Hope it's OK to post in here with a similar problem; If not, I'll move it elsewhere.
I'm new to RPI and have recently been gifted one which I've installed xbian on to replace the desktop pc upstairs as a front end. I'm having similar trouble with VNC.
I'm running VNC Viewer 6.0.1 on my windows machine. When I try to connect to the RPI I get the following distorted output:

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If I then restart the VNC service by going through system> xbian conf > services> selecting vnc-server and restarting, it then works as it should when connecting from my windows machine...until the next reboot. VNC Viewer from my iphone constantly connects and then disconnects regardless.

Any suggestions? I've updated everything I can through the OS GUI but am now at a loss. Any help gratefully received. (It might be worth bearing in mind I'm not that techie so step by step instructions would help if you have the patience)

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......It's probably also worth mentioning that if I "try" to connect to it whilst the RPI is booting up (before it gets to the xbian splash screen) it works OK. Not very practical though!

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oh....and running Version: 2.4.2-1494784542

I re-read the thread and also changed AUTOMODE from 1 to 0 in /etc/default/vnc-autores. Still no difference.