i have solved the problem,

The component installer page for joscommunity needs more than 8M memory because of all the components installed.
My host has a memory_limit of 8M set in the php.ini file

. I am on shared hosting so cant change the ini file. I have found a small work around though.
in the file: administrator/components/com_installer/component/component.php, enter the following code:
ini_set("memory_limit", "16M"); at line 23, just before the require_once function.
I dont know if this will also fix the main menu problem. I havent had it. I would advise using the same code in the relevant filefor the create menu function.
hope this helps you aswell dehydratedchicken