Power to the CPU = no start up.

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Jeff Kaos

Jeff Kaos

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Apr 6, 2014
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When I turn on my computer nothing happens. I tested my power supply unit and determined that it was dead. I ordered a new PSU and hooked it up and still nothing happens. But when I started troubleshooting connections I noticed that if I plug in my 24 pin connector, my DVD drive and my HDD but NOT the 4 pin cpu power my computer starts up fine aside from no cpu which pretty much means the computer is useless. I've built a lot of PC's, probably over 200, and I've never had this happen on a build before. I tried re-seating the cpu but that didn't do anything. I'm at a loss as to what's going on. I'm thinking that there's either something wrong with the mobo or the CPU itself or both. If anyone knows what this might be I'd appreciate some help.
 
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Jeff Kaos

Jeff Kaos

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The system is an off the shelf CyberpowerPC Gamer Ultra GUA880 that I received as a Christmas present that I started upgrading with an Evega Gforce GTX 750 ti gpu. It still has the stock mobo/cpu which the mobo is a Gigabyte GA-78LMT-S2 and the CPU in an AMD FX 8120 8-core processor. The original PSU was a 500 watt piece of junk that I knew was going to go but I didn't have the cash to replace it until now and the new PSU is a Corsair RM 750.

The system originally died last weekend when I left it running for a few hours while I was doing some errands with my wife. When we got home from the store the PC was shut down but some of the LEDs on a few of the USB devices (headphones, USB wifi receiver) were still lit so I thought it went into sleep mode. When I tried to power it up one of the case fans lit up for a second (it has a light in it) and the cpu fan spun for a second to but then nothing. I took the unit to my work, where we build PC's for the medical industry, and tested the PSU. It was dead. I grabbed a scrap PSU from the recycle bin that I knew still worked and plugged it into the motherboard but there wasn't a 4 pin connector on the scrap PSU so I left it and the machine powered on ok. So my friends and I figured it was the PSU so I ordered a replacement. When I went to plug it in everything happened like I said in the OP.
 
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HiTechObsessed

HiTechObsessed

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The 4-pin is essentially supplemental power. The motherboard can supply up to 75w of power to the CPU, so unless you go over about 60% load with the 8120, you can get by just fine with no 4-pin.

However, the motherboard you have is extremely lacking in power delivery for an 8-core CPU with only 3+1 phase power delivery. You may have damaged something on the motherboard.

In addition, 750w is extreme crazy overkill for that build. You'll only be using around 175w at full load, which will actually put more stress on the power supply and make it die quicker than a quality 500w power supply.

Since trying the replaced power supply, have you tried a known-working one again?
 
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Jeff Kaos

Jeff Kaos

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I don't have an extra working PSU and I'm on a short vacation until next week which is when I 'll be able to try another PSU. I had a feeling that the budget mobo was incompatible with the CPU. The specs on the build on Amazon, where my wife bought it, lists a quad-core processor but when I looked at the windows specs it had the 8 core processor in it. I didn't know that about the 750 watt psu though and I thank you for the heads up. I grabbed the 750 because it was on sale from the store I bought it from and to be honest I didn't know about it stressing. I figured a 750 would be good in case I wanted to upgrade to a better GPU in the future. Can You reccomend a decent 500 watt PSU that's reliable?
 
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HiTechObsessed

HiTechObsessed

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XFX is built by SeaSonic, and one of the best brands out there. This is fully capable of powering any single GPU you can hook up to it:

PCPartPicker part list / Price breakdown by merchant / Benchmarks

Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($49.99 @ NCIX US)
Total: $49.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-10 17:28 EDT-0400)

Kinda sucks you can't try a new one :( But this is one of the reasons we try to steer people away from pre-builts, as they usually skimp on stuff like the power supply and motherboard. If it does end up being a bad motherboard, I would recommend at least an 870 or up (depending on budget), to get sufficient power delivery.
 
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Jeff Kaos

Jeff Kaos

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I'm actually thinking about cutting my losses and just scrapping the AMD stuff and going with Intel, which is what I wanted to do before I got this system. I want to try and salvage as much as I can in order to keep costs low. If swap out the AMD chipset will I be able to use the DDR3 ram from the current setup in an Intel setup? and I'd also like to know if I can use the same boot disk to load windows into the new mobo/cpu. The boot disk is CyberPower branded and has all the drivers for the current build on it plus the windows 7 home edition. I've never used a boot disk like this. At work we load an OEM Windows disks and then plug the system into our network which then automatically flashes BIOS and loads all the driver images.
 
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HiTechObsessed

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Yeah, you can use the same hard drive, same windows disc, same RAM, same case, same PSU. You'll have to completely wipe the HDD first, and you'll want to get the drivers from the manufacturer, not the disc. What kind of case do you have, and what kind of budget would you be looking at?
 
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Jeff Kaos

Jeff Kaos

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I'm thinking about trying to keep it as close to $200-$300 (preferably closer to $200) as possible for a mobo/cpu combo. I'm not sure about the exact model but the case is a Cooler Master mid size tower with 3 case fans and it looks like a fairly standard case. The current mobo is a "mini" so I know I'll need to make sure about the case and whether it can hold a larger board but I don't think it will be a problem. I'm also going to return the new 750 watt psu and look into the one you suggested. Before I wipe the HDD I'll take it to work and try and dump the documents folder onto another drive because it has a lot of pictures on it and I only have about 2/3 of them backed up.
 
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HiTechObsessed

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You could go something like this:

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4430 3.0GHz Quad-Core Processor ($180.49 @ Amazon)
Motherboard: ASRock B85 Pro4 ATX LGA1150 Motherboard ($64.99 @ Newegg)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($34.99 @ Micro Center)
Total: $280.47
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-11 10:05 EDT-0400)

The i5 will actually give you better gaming than the 8120, and being an Intel chip, has much better single thread performance, and will operate cooler and quieter. The 500w EVGA PSU is a pretty good PSU, and will be plenty for your needs. This system would run around 200-225w at full load, putting you right into the power supply's peak efficiency range.
 
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