1) To enter bootloading mode you need to unplug power, and press and hold pushbutton B2 while plugging in a USB cable. Then release B2 within 1-2 seconds after the USB is plugged in. This way the controller will appear as a USBasp device. The screen should remain off. If the screen lights up, the controller will not appear as a USB device, and you need to repeat the procedure above.
2) The ‘Disabled’ message means the controller operated has been disabled. You can re-enable it either by pressing and holding pushbutton B1 for 2-3 seconds (until the ‘Disabled’ message goes away), or you can enable the operation through the web interface. These have all been explained in the user manual, available at http://www.opensprinkler.com -> user manual.