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Login to your controlpanel
Click the domain sumondo.co after logging in
Click the Statistics/Statistikker icon
Now you can view your ERRORLOG and with your webdesigner correct the problem (if shown).
If your website is a WordPress based website and your TEMPLATE is causing problems, log into your server with your FTP program (FileZilla is a good choice) and rename the folder containing your WordPress template, when WordPress cannot find the selected template it will use the default one. If it is a plugin you can also rename the plugin causing the problems.
Plugins are in the /wp-content/plugins folder
Templates are in the /wp-content/themes folder
BACKUP/DOWNLOAD all your files BEFORE deleting or renaming any files/folders.