I saw in your reply to cwhale in this forum that you updated El Capitan - was this an update from an previous version of El Capitan or an upgrade from Yosemite.
If it was an update would it be possible to upgrade from Yosemite to El Capitan and if so what extra things are needed to allow booting to El Capitan.
CPU: AMD Athlon II X3 445 3.1GHZ
Motherboard MSI 770-C45 AM3
GPU nVidea Geforce 8400GS
LAN Integrated RTL 8111DL
Sound Integrated Realtek ALC888S/ ALC885USB
4 Hard Drives with different OS'S Win 7, Win 8.1, MacOS X Yosemite and MAC OS X El Capitan 10.11.3
Have a another PC with Win 10 on it.
Bootloader: Enoch for El Capitan
I use USB Wacom Tablet and Pen instead of a mouse plus a USB Keyboard