bitnami wordpress stop working

hi there i am using a micro instance on aws to run my small website, it was working perfectly from last 4 month suddenly i found that it stop working and give me 404 on every page, i checked the error log there is not error found but when i check my access_log i found continuously hit from same ip on my xmlrpc.php file and takes 100% my cpu usage when restart my all services it start working but few minutes and stop again.

aws micro instance + bitnami wordpress

please help

thanks
n3RDY