Sapphire 4870 three red lights no display no boot

[rlfenfl]

Hi,

I built my PC 1 month ago, and had been using it without a problem. However, recently when I turned it off and on, there was no display at all and no boot. And I couldn't turn it off without shutting down PSU. A few days later when I tried again, sometimes everything was OK. Once the PC started, there was any problem at all. But now, it is not booting and has no display.
I have tested it with my old video card Geforce 9500GT, and there was no display as well.

After I searched in the forum, I found that my video card (sapphire 1gb 4870) has three red lights on the back of the card. The three red lights existed until I shut down my PSU.

I figured out later I didn't set up the memory as the company said like 2.1V, 5-5-5-15. Because the PC worked well last one month, I didn't notice that I should have changed it in the bios. When the PC could boot by accident, I changed the voltage and others as the company said.
But my PC has not been booted gain when I tried to turn it on after changing the bios.

Here are my specs.

AMD Phenom II X4 940
Gigabyte GA-MA790X-UD4P
G. skill 4GB (2x2GB) DDR2 1066 (PC8500)
Western HDD 1TB
Corsair PSU 750W

Since the PC could start sometimes by chance (I don't understand why...) after a few days later when I didn't do anything on it, it is hard to figure out what is wrong. Motherboard? Memory? Video Card?....

I would greatly appreciate to get any advice or help on it.

Thank you so much in advance.

 

[alvine]

3 red lights mean you didnt plug both power connectors to the card i remember i once forgot to plug both pcie power connectors and i only plugged only one and i got those 3 red lights as well

 

[belial2k]

Check your connections, if everything was working fine, then suddenly quit without you doing anything, most likely problem is power supply failure since you tried another card and it also did not work.

 

[rlfenfl]

3 red lights mean you didnt plug both power connectors to the card i remember i once forgot to plug both pcie power connectors and i only plugged only one and i got those 3 red lights as well

Thank you, alvine.

I have connected the two power connectors to the card and have used it properly.
It failed to start suddenly when I tried to turn it on again. Weirdly, it sometimes started by chance after a few days later without doing anything.

Anyway, thanks for your advice.

 

[rlfenfl]

Check your connections, if everything was working fine, then suddenly quit without you doing anything, most likely problem is power supply failure since you tried another card and it also did not work.

thanks, belial2k.

Hopefully, there would be no power failure... is there any way to test the psu without testing after changing all other parts?

or is there any chance to have problems about the memory or motherboard?

 

[belial2k]

Its about 75% likely its your PSU from what you have described. The best way to test it is to replace the PSU with another one that is capable of powering your system. You have already ruled out video card error, and MB, hdd, memory, or other hardware error doesn't usually cause the problems you described.

 

[rlfenfl]

Since the PC had been working, the memory and mother board may be ok. I'll try with another PSU.
Thanks, belial2k.