my site down due to the handler

[dreamnet]

My site down again
server unstable
I use .htaccess
AddHandler application/x-httpd-php5 .php

if I get rid of this works fine under php4
if I add this line, unstable, alway said internal 500 error

I need some function which only in php5

[kmaw]

Email support@hostgator.com
There must be something else wrong, adding that shouldn't cause 500 errors.