Can log into site but not admin dashboard. Get internal server error

Yesterday, attempted to complete site verification for google webmaster tools. I added the following as instructed by google to the header.php file between the <head> and before <body>
(<meta
name="google-site-verification"
content="Zou7Mx6xR2vZPPKwLKVEPK6qF7ZH4qBL11ak1vRsuy4" />:wink: the the meta google.

First I received this warning and my site was unable to be viewed. Only this warning and fatal error came up.
Warning:
require_once(/home/ldiederich/ecraftandshare.com//wp-admin/includes/plugin.php)
[function.require-once]: failed to open stream: No such file or directory
in
/home/ldiederich/ecraftandshare.com/wp-content/plugins/marketpress-frontend/mark
etpress_frontend_admin.php on line 139

Fatal error: require_once() [function.require]: Failed opening required
'/home/ldiederich/ecraftandshare.com//wp-admin/includes/plugin.php'
(include_path='.:disappointed:usr/local/lib/php:disappointed:usr/local/php5/lib/pear') in
/home/ldiederich/ecraftandshare.com/wp-content/plugins/marketpress-frontend/mark
etpress_frontend_admin.php on line 139

So I disabled frontend marketpress using ftp.
The site came back up but when I went to view the dashboard I got a 500 internal server error.

I then went back to ftp and disabled all plugins: still get 500 warning when logging into wp-admin.

Went back to ftp and disabled twentytwelve theme to revert back to default theme and then got a white screen.
contacted host: still waiting for a response.
I reenabled twentytwelve: site is up without marketpress frontend which I still need. I can log into site but can't access dashboard.
Is there anything I can do? Has anyone else had a problem like this when verifying website with google?