If you are installing Magento and you have uploaded your Magento files to your host and just when you are about to run the Installation wizard, you get “500 Internal Server Error”. This error is because of the inappropriate file permissions.
To overcome 500 Internal Server Error :
change the folder permission of below folder to 777
change the file permission of below files from 664 to 644
index.php (main index file in magento root folder)
downloader/index.php ( otherwise if you will try to access System > Magento Connect >Magento Connect Manager (after magento installation) by logging to magento admin, you will get 500 Internal Server Error.)