Cannot wake up MBP from screen saver, have to hold down power button and reboot almost everytime

Hi, I've gotten a 15-inch, Mid-2009, 2.53-GHz Core 2 Duo, 8-GB RAM MacBook Pro with a 320-GB standard HD and OS X El Capitan 10.11.4 that has issues in waking up from the screen saver.

System is set to automatically start the screen saver and lock itself up (require a password) after 3 minutes of inactivity (FileVault 2 is enabled).

However, when trying to wake up from sleep (screen shuts down after 5 minutes), if I click with the mouse or type anything with the keyboard, I get the spinning ball that lasts forever. I don't even get the "Type your password" box with my username.

So, I have to hold down the Power button, shut down the MBP, and reboot. Till next time!

How do I get around this?