.htaccess problems, permalink won’t work

I can’t seem to get permalinks to work on my blog. The regular ones work just fine, but when I try to make them pretty, it says it can’t write my .htaccess. That’s fine. But when I try to create an .htaccess file and insert the wordpress code, I get a 500 error on every page, even just wordpress/index.php or wp-admin, etc. All the pages stop working. There is no default .htaccess file on my host, so I know it’s not a problem with me editting it. Any help?