keysync

I was editing default-widgets.php and saved it.
Now when I save something, or try to log out or whatever I get a white page. And this is filling up the error log just about as fast as I can clear it.
Any ideas?
I've checked for a space before the opening < and it's fine.
No idea what to do. I really don't want to start over...

PHP Warning: Cannot modify header information - headers already sent by (output started at /home4/mechank1/public_html/wp-includes/default-widgets.php:1) in /home4/mechank1/public_html/wp-includes/pluggable.php on line 866

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