503 error caused by corrupted file?

I didn't know where else to post. && sorry if this is the wrong place to post this.

I've tried support forums for the script(s) I recently installed, but nobody seems to know whats up. Anyways, I just got my own domain about a week ago from ActiveWebHosting. Everything was working great. The only scripts I have installed are CuteNews & Simple Machine Forums (SMF). After installing SMF it worked fine for a day, but not if I go on it for more then 5 minutes or so, I get a 503 error. But it also happens on my main page without the forums. I contacted my host and they said my CGI & everything is running fine & they aren't doing any updates. Someone else told me that I may have a corrupted .htaccess file ... If thats the case, how would I edit/fix that? Does anyone know? Or are there any other causes/reasons for a 503 error?