Dell inspiron 620 doesn't turns on

If its a problem like that it could be the power supply. If you could borrow a power supply from a friend, or just buy one temporarily and see if thats that problem.

I had the same problem. Tried unplugging everything, removed battery, different power supply, jumpered reset switch. Nothing worked. I then jumped the number 16 connection wire from the 24 pin motherboard connection from the power supply (green wire) and it can back to life. Can't duplicate the cause of the problem. But it's working now and I can turn on or off from the front switch. You might try this, but be careful you could short out your motherboard if you choose the wrong wire. Power Supply On (active low) (#16 wire Green) on 24 pin connector. Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF.