cuoresan on "ERR_EMPTY_RESPONSE when try enter to Admin-panel"

Hello, i have trouble, when i try login into admin panel, chrome show me "ERR_EMPTY_RESPONSE" error, but main page working, i try different browsers and devices, use other internet connection but no change, how i can fix this ?
php 5.3.3
mysql 5.1.66
apache 2.2.16