Wordpress site keeps going down with a 500 Error...

Wordpress website site keeps going down with a 500 Error. It will be up for a certain period of time — an hour… a day.... 2 days... 4 days.... — it varies. Then, all of a sudden, it will go down again. My hosting company seems to think it is related to the .htaccess file and that that file needs work. When the site goes down (as it inevitably will) I can get it back online again by renaming or deleting the .htaccess file (take your pick) it goes right back up again. But it won't last. Eventually (usually sooner than later) It will go down again. That said, I have replaced / deleted / re-written / saved as new / restored from backup this file more times than I can count. This is super embarrassing / horrible for business. Today have deleted all non-essential plugins. My host reset the Apache service this morning. I changed my wp cache plugin settings (for better or for worse?) but the site still went down a few hours later. Please let me know if you can solve this quickly! Thanks.