Help! Monitor wont turn on

Hi everyone, my brother has been having issues with his pc and he took mine. Ive been trying to repair his but with no success. The Cpu turns on with the fans and the lights, the keyboard turns on sometimes, but the mouse and the monitor doesnt turn on. Ive tried removing and cleaning the rams and switching spots, Unplugging the battery and waiting and turn back on, Removed the reset cable and tried, changed monitors, Switched rams. Nothing has worked yet, is it time to throw it out? He was working fine and suddenly it turned off 2 days ago and since then it wont fully turn back on. Please help. Thanks!!