HELLO, EVERYBODY! PLEASE HELP! MY LAPTOP WILL NOT TURN ON

Hello,
Please help! my laptop won't turn on when I push the power button. I have a Toshiba Satellite L455D-S5976 and its about 6 - 7 years old (I know is old, but was working just fine). When I press the power button the fan spins for about 1 second then stops and that's it nothing else happens; some system indicator lights turn on like the AC power light, the On/Off light and the battery light but not the HDD light. Now these are the things that I've tried so far: 1) Removed the battery and the power supply and hold down the power button 30 seconds. Then plug in the AC adapter and try to start it. 2) Reseating the ram. 3) Replaced motherboard, Battery & Laptop AC adapter. I don't know what else to do. What do you guys think? could it be a bad ram stick or a bad HDD?