benxx:
I even had downloaded and pasted files from GitHub - esp8266/Arduino: ESP8266 core for Arduino to my Arduino/hardware/esp8266com/esp8266/ folder.
benxx:
from C:\Documents and Settings\Compaq\Local Settings\Application Data\Arduino15\packages\esp8266\hardware\esp8266\2.3.0\cores\esp8266\Esp.cpp:24:
Did you try to do a manual and a Boards Manager installation? Because your first statement indicates a manual installation but your output shows you did a Boards Manager installation. If so you should delete Arduino/hardware/esp8266com/esp8266/.
Please use code tags(</> button on the toolbar) when you post error/warning messages or any other console output.