Fatal error after installation

Hello:
I have installed wordpress manually in my account but it is unresponsive and
when I want to do any thing it give me the message :” Fatal error: Allowed
memory size of 67108864 bytes exhausted (tried to allocate 122880 bytes) in
/home/a5608264/public_html/wp-admin/custom-header.php on line 544″ and I
don’t know what to do?
Yours,Mosbah