Dell Dimension E510

Hi everyone,

I have 10 year old Dell Dimension E510. It was working fine until 3 days ago when I was watching video on youtube, i heard weird sound and then pc turned off by itself. I turned it on back with no problem and then start watching the video but lost power again in a few minutes. I tried to turn it back on but this time it wasn't booting, only hear fan is running and on the monitor "no signal". Only 1, 3 and 4 led lights are on in the front panel when it's on. Number 2 is off. I was told motherboard is dead and need to replace, some one else said I need a new power supply. So I have no idea what should i do. I hope someone can help me on this forum and fix my pc with spending not much on old pc. Thank you in advance.