Error establishing a database connection

Hi all i am new here and in my website http://makeadvice.com/ i am getting error that “Error establishing a database connection” but kindly note in account that i am not getting this problem continuously some time my we site is working fine and after 10 minute i gets the same error message “Error establishing a database connection” or blank page . now a days the web site is also slow before 4 to five days ago it was much fast and quickly open while click on any where on the site i thought that this problem is taking place because of server down but i don’t know that why this problem is taking place and some time it’s working very good kindly help thanks.