Just replaced Mobo, now Comp doesn't turn on

Do you have the 4-pin molex connector connected from the power supply to the plug near the processor on the motherboard?

 

You didn't tell us your power supply wattage and brand.

After checking the specification, there is a possibility that your video took most of the power than PSU can gives.

 

have you try to replace with some new power supply? or some others power supply with more high power than you use now? Have you check your power supply in other cpu's? And perhaps just like Tmagic650 says, perhaps the motherboards have the 4-pin molex connector that you need to connect.

 

Yeah, it has the 4-pin and it is connected. power supple is 450 watt, and the only other one i have to test is a 250 watt. the board has no on board video, and i took out the graphics card, but no boot. Would i be able to use the 250 watt for testing purposes, even though the board says it needs at least a 300 watt?

 

Actually, it should be at least 350W with a least 32A 12V rail support for your video card.

 

read: https://www.techspot.com/vb/topic55506.html

 

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here's another sample. Perhaps looks similar to your cases. I'm using an MSI 945PL-Neo with processor Intel Pentium D 2.8 Ghz + memmory Dual channel 1 Gb+ MSI Nvidia GeForce 6600 (video card) + Enlight PSU 500 W.

The problems occur 3 months after my friends using it. The problems look similar to your case, when i turn on the pc, the processor fan kicked for a sec, and the power LED flashed on, and then went off almost instantly. I tought it was because the dust, then i try to clean it off, but still, nothing happens. I Tought it was the PSU, then i try to replace the PSU and i try the old ones in another PC. The result is, that the old PSU turns out to be OK in another PC, instead the other one shows nothing, i mean nothing change when i put on the new PSU on the MSI board. My Conclusion then the board is damaged (tough my friends didn't use any overclocking system on that PC) and then i replace it (Still got a guarantee), and the problem solves.

Perhaps you need to replace your boards too, tough it's a new one, but there is no 100% guarantee it will go smoothly.

What i'm trying to tell is, it is good to use a good and pure watt PSU, and it is good to use a great brand hardware. But still, a factory failure is something that we cannot avoid.