GX620 will not boot-no lights, no beeps

The key is that it takes a minute for the motherboard light to go out. It should go out in about 10 seconds with the button pressed. Therefore, the button is not making contact. The switch itself could have failed, that's uncommon, but the front panel board is the cheapest replaceable part.  First, reseat the cable to the front panel board.

 

I forgot exactly what the 620 chassis looks like. But recent Dell chassis have had an issue with the bezel button not aligning with the switch. When this happens, you will not be able to feel the switch click when the button is pressed.

 

If you have this chassis and this issue, it can be remedied by loosening the screw above the button on the side chassis flange, holding down the bracket, and retightening. Seeing as how it used to work, it should be within range of jiggling the bracket such that it works again. If not, replace front panel board.

@ x_lab rat

Thanks for the help. After I posted, I tried a board and cable from another computer and it did not work either. I also eliminated any mechanical problems with the switch by using the poer button directly.

 

 

I can't explain why the light is staying on a minute then.  That's not right.  But it may be related.

 

You substituted a known-good power supply and frontpanel board w/cable.  So it's not those.  I don't see anything left but motherboard.  The attempt to turn power on is a low-level chipset function.  But low levels can fail just like high levels can.  The low-level chip is run by a crystal--it's actually a primitive computer within a computer.  If the crystal stops, the computer stops and will not respond.  The crystal itself is a $1 part, but Dell doesn't sell sub-parts, only assemblies.

 

A shop can replace the crystal, might charge as little as $60.  But if that's not what it is, and they spend hours figuring out what it is, the cost exceeds the price of the whole motherboard.  Thus, economically, repairing motherboards is not practical and they are almost always replaced. 

disconnect cables from the hoard drive. Tehe power on. Then what happnes?

@SpeedStep

 

Same thing. Completly dead, still get motherboard light on only.