i've checked the error.log and found this:
2014/12/21 11:57:12 [emerg] 9835#0: bind() to xx.xx.xx.xx:80 failed (98: Address already in use)
if I use the following, it is working fine:
rewrite !\.(js|ico|gif|jpg|png|css|pdf|mov|mp3|eot|svg|ttf|woff|otf|txt)$ /index.php break;
rewrite /$...