I have a dell optiplex gx620 and it wont turn on

As you can imagine, this is not simple thing to diagnose.
First, we need to try Dell's steps to fix...
Remove non-essential peripherals…
Except for the monitor, keyboard, and mouse, remove all external peripherals including:

• Scanner
• Printer
• Modem or Network cables
• Personal Digital Assistant (PDA)
• USB flash drive or other external Hard Drive
• Any other external devices (e.g., USB-attached devices)
• Remove the computer from the docking station, if you are using one

Remove non-essential peripherals…
Except for the monitor, keyboard, and mouse, remove all external peripherals including:

• Scanner
• Printer
• Modem or Network cables
• Personal Digital Assistant (PDA)
• USB flash drive or other external Hard Drive
• Any other external devices (e.g., USB-attached devices)
• Remove the computer from the docking station, if you are using one

Try rebooting. If that doesn’t work, Dell states you need to do the next step.
Remove and Reseat Basic Hardware items:

1. Power Cord
2. Memory
3. Hard Drive

At this point, Dells says if that fails contact them.

If my hunch is correct, you may have something on the motherboard shorting a connection or you have a blown capacitor. Get some “canned air” and blow out the computer thoroughly. Some people have reported the same symptom having dust or other debris causing the issue, so give it a good blowing out,

At the same time, inspect your motherboard thoroughly for an anomalies. If you see anything resembling the picture below, you have a serious motherboard problem which will require replacement.

Sir,
It seems that you computers power supply has got damaged or burned you will be required to replace your power supply it would be better if you buy the 400 to 500 W power supply.

ok if the ups is not the problem you can try looking in the back of your pc you will see a little orange or red swith that can be clicked side to side or up and down. this is your US and over seas power seting. if its on 115 try clicking to 220/230
now try booting if it still does not boot return it back to 115 and pull the main power connector from the motherboard,.. wait 5 minutes to release and power the board may have. reconect power connector to motherboard and boot pc.

My eMachine T2542 keep blinking green. I thought it was a bad PSU but I tried a new one and that didn't fix the issue any answers to what's causing this problem?