PC will not start, fan starts to spin and it stops

bad motherboard

Reseat the RAM. That should fix it.

If the problem persists, then your power supply is likely dying. My guess would be the RAM.

Hello
It almost sounds like a mistake at the pc start switch and reboot switch.

Check that you have your pc start wires from the front start button of the case, in the correct spot on the motherboard.

Also remove the memory sticks and reseat them.

The green light on the motherboard is good it means your getting power from the power supply.

The start and reboot switch wiring can be tricky if one plug is in the wrong spot on the motherboard.

That switch is there to select between European and US voltage - if the pc has worked before then leave it as it is. Change it to the wrong setting and the power source will be fried.
Your pc doesn't start because you have a hardware fault.  Disconnect the data cable from the hard disk and try again. Next you must test the power source itself , outside of the pc - take it out then connect the green wire from the big connector to the black wire next to it; if the fan of the source doesn't start then it's fried, replace it. If it does then you must try the other components. If you haven't done that before , or if you don't have other components to swap for testing ,  then it's time to take it to a shop, nothing more you can do to it

1>NEEDS TO TRY RESEATING OF THE RAM(SWAP THE RAM WHILE PLACING THEM BACK IN) AND THEN TRY TURNING ON THE COMPUTER
2> IF THIS DOES NOT WORK THEN NEEDS TO REPLACE THE MOTHERBOARD

BEST OF LUCK

the RAM may be corrupted or not properly installed into the slot. also check if the processor fan is working properly.

Flickering LED means power supply is overloaded with something. It might be inside of the supply, but sometimes it is something else. Try that:
1. Disconnect everything from the motherboard except power supply and power button;
2. Disconnect all power connectors from all drives;
2. Remove any cards from the motherboard so all you have is power supply and motherboard with CPU and RAM, nothing else. You can keep connected the monitor and keyboard;
3. Press Power button. Will motherboard turn on normally?

If no - check electrolytic capacitors especially around the CPU, if some of them are "popped" replace them.
If yes - connect drives and cards one per time to localize the problem.

Check the power supply unit.

turn on your computer and do nothing,, when it seems the computer stop running key in fn+f4.

try to get to the jumper next to the cmos battery in the mainboard. by changing its position for some seconds while power is off and putting it back , cmos is cleard. start the board hit delete to enter setup and exit saving chages.