Hardware and performance

Nothing ventured nothing gained - I tried clicking the Test button in the XMLDB editor which makes it do something and then it finishes up with the word 'MySql server has gone away' which isn't very reassuring.
With debugging turned on it gives me reams of closely packed type containing all kinds of strange looking symbols below the phrase 'MySql server has gone away'. Something tells me this isn't right.
At the end of the type there is a list of 42 normal looking statements about the database then the 43rd item saying MySQL server has gone away and then under that more of the debug code which says:
MySQL server has gone away

SELECT * FROM mdl_block_instance WHERE pageid = '0' AND pagetype = 'admin' ORDER BY position, weight

• line 677 of lib\dmllib.php: call to debugging()
• line 601 of lib\dmllib.php: call to get_recordset_sql()
• line 882 of lib\dmllib.php: call to get_recordset_select()
• line 907 of lib\blocklib.php: call to get_records_select()
• line 440 of lib\blocklib.php: call to blocks_get_by_page()
• line 2690 of lib\adminlib.php: call to blocks_setup()
• line 111 of admin\xmldb\index.php: call to admin_externalpage_print_footer()

Well as this all means very little to me, except that it is clearly not right, I'm off to investigate. Any suggestions greatfully accepted.
Thanks