Suddenly unable to get in login page

I installed wordpress from Bluehost cpanel for 8 of my domains. Today, for no particular reason, I’m unable to get into the log-in page at all.

When i key in my usual mysite/wp-admin, it just gives a blank screen (on Google Chrome, it shows the error: The website encountered an error while retrieving mysite/wp-login.php?redirect_to=http%3A%2F%2Fmysite%2Fwp-admin%2F&reauth=1. It may be down for maintenance or configured incorrectly.
Error code: 500)

This is the same for all my domains. Did a check with Bluehost but everything’s fine. Tried updating one of the domain to 3.6 but still doesn’t resolve.

Other troubleshooting includes changing the .htaccess file.

Anyone can offer some solution?

Thanks in advance!