Where to start problem determination with Wordpress Database

[searchsupreme]

Wondered if someone could help me please. I don't mind admitting I'm completely out my depth.

I have a repeating issue that takes out my wordpress database periodically for the site refurbished-phones.co.uk

I don't know what triggers this 'meltdown' but neither my own browsing of cpanel features nor assistance from web host have come close to identifying the issue. The host simply says something is causing the database to over load.

Can someone please recommend how to start problem determination to help narrow down the cause? I don't know where to start

If it helps...

I use the Genesis Lifestyle template and have the following plugins active:

Askimet
Contact Form 7
Custom Field Template
Dynamic Content Gallery
Genesis Simple Hooks
Genesis Simple Sidebars
Google XML Sitemaps
Official Statcounter Plugin
Redirection
WP-DBManager
WP Custom Search

Any ideas greatly appreciated :)
Thanks