Backend page is blank

Hi There,

i am having issue at backend…it happened quite a while and i asked hostgator to solve this problem but they are helpless and told me to post here…

seoaustralian.net.au/rtilkc57tp_sd34k/

you can check here…it seems that it has got something corrupted…front end is working fine but i am not able to see the login screen so if anyone can help me plz…

thanks in advance
Harry