Missing Header

  Okay I don't know what happened but my site logo and quotes module have disappeared from my site pages, can anyone tell me what may have caused this problem?  The entire head section above the top banner position is gone no white space at all.  Site page starts at top banner which has never been changed.  

I found that my logo had somehow vanished from my site admin so I tried to reupload the logo image  and received this error message at the top of my page

Warning: getimagesize() [function.getimagesize]: Filename cannot be empty in /home/site/public_html/administration/basic_settings.php on line 309

Warning: Cannot modify header information - headers already sent by (output started at /home/site/public_html/administration/basic_settings.php:309) in /home/site/public_html/inc/admin_design.inc.php on line 56

but logo and Quotes module have returned.

Can anyone explain what may have caused this & how to prevent it from accurring again?