If 'you site fails' when you place an htaccess in your root, that means that the .htaccess is actually being read, and thus, you can use it. However, there is something magically wrong in the file, which causes trouble when loading your file.
I am certainly not and apache config expert, but you can have a look at your log files, and see what the apache error log sais.
If you do no tknow where to look, and the server / control panel does not show any clear signs, you could contact the hosting company, and ask them how to check the apache error logs.
I usually empty the log file, load the page that gives me errors, and then download the logs. Usually you'll only have 1 page load in the log (Which may consist of many many lines of messages!) and that makes it easier to spot what went wrong.