Fatal error while changeing theme website doesnt work help!

FTP into your site (or use whatever file management application your host provides) and delete the /wp-content/themes/k2 folder.

I did that, the notice went away but now nothing is loading up

Is the default theme installed?

Also try resetting the plugins folder by FTP or phpMyAdmin.

yes the default theme is still there, and btw I unactivated the plugins before I changed the themes, (or was trying to)

Also renamed the plugins to plugins.hold to stop the plugins from working, that didn’t do anything

I’d still try resetting the plugins folder – preferably using phpMyAdmin if you can. Sometimes, an apparently inactive plugin can still cause problems.

renaming the plug in folder will not do the same?

It’s not as complete a reset as the phpMyAdmin method.

still not working

acctually now it is prompting me to reinstall word press…..am I going to have to reinstall and loose everything?

anyone?

Why not re-upload the wp files and directories through FTP (but not wp-config.php).

reloaded the oem theme now it works,

but I loaded f2 theme and now I get

Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /homepages/37/d317353578/htdocs/wp-includes/widgets.php on line 825

on the side, what does this mean? Is there something I need to change in the code again in the plugins part?

also all my pages are gone, are they really gone or do I need to do something to get them bacK?

Try deleting the wp-content/themes/f2 folder.