Cannot access Dashboard after Jetpack

Hi there,
I am trying to get my site italianviaskype.com work better on mobile. In the procedss, I tried to configure the JetPack plugin. Now, when I tr, I cannot get to my dashboard anymore and I get the following message
“Warning: mysqli_set_charset(): Error executing query in /hermes/bosnaweb10a/b2723/ipg.italianviaskypecom/wp/wp-includes/wp-db.php on line 818 Warning: Cannot modify header information – headers already sent by (output started at /hermes/bosnaweb10a/b2723/ipg.italianviaskypecom/wp/wp-includes/wp-db.php:818) in /hermes/bosnaweb10a/b2723/ipg.italianviaskypecom/wp/wp-includes/pluggable.php on line 1174”
Can anyone help, please ? Thanks in advance.