When your website goes down there are a few simple steps you can do yourself to try and diagnose the cause and point you in the right direction to resolve the issue.
1) First check if you have kept up payment for the service you are using. You would be surprised at how many times when things go down it is due to non-payment and the consequent suspension of services.
2) Check if your domain registration has expired. You can check whether the domain registration is still active by going to http://nic.uk , or other whois servers on the Internet. If the domain registration has expired and the domain provider is not ByteHouse contact your domain provider.
3) Check that the DNS settings for the domain are configured properly.
4) Check your disk space as sites and servers go down when you run out of disk space, whilst running low on cpu and RAM slows down your site or server.
5) If all the above do not help you identify your problem it is helpful to check your error log. If using Plesk Control Panel the error log is located in the advanced operations section of your site in the Websites & Domains tab. This will allow you to pinpoint the cause of your problem and for you to resolve your issues.