New build, constantly reboots after successful POST

[breakingspell]

I've built around a dozen machines, but this one has me stumped left and right. It's for a client, a sweet old lady that was limping along with an old Compaq, so it's nothing special, the specs are as follows:

CPU: AMD A10 5800K
Mobo: Gigabyte GA-F2A88XM-D3H
RAM: Crucial Ballistix 4GB
PSU: EVGA 450W (previously Corsair CX430M)
HDD: WD Caviar Blue 1TB
GPU: Asus Radeon HD 6450
Case: CM N200

I initially assembled the machine last week, but while trying to boot to my Windows 7 USB, the computer would constantly reboot, even while sitting in the BIOS setup. It POSTs without issue, but after a short amount of time, it will cycle power and POST again and again. I've tried using a Windows 7 CD, Windows 8.1 USB, and my handy Hiren's BootCD, but the computer will always reboot shortly after selecting them in the boot menu.

I've checked and double-checked every connection, re-seated every component aside from the CPU, ran tests on the memory and HDD on my own rig, and made sure every standoff was properly screwed in, sometimes it would last long enough to get to the Windows 7 setup, but then it would reboot during the setup, or throw BSODs (0xD1 and 0x24, which correspond to completely unrelated issues). After hours of troubleshooting, I decided that the motherboard had to be bad, so we RMA'd it with Newegg and waited a week for the replacement to ship.

I went back out today and installed the new motherboard, to find it had the exact same issue. Fiddling with it more, I noticed that the main power rail was having a tough time getting a solid seat on the board, so I went to Micro Center and picked up an EVGA PSU, and while it has a solid connection, the issue still persists.

This issue occurs on a minimal configuration, with no PCI cards, SATA or USB devices, and only 1 stick of RAM in every slot. At this point, it couldn't be anything else but the CPU, but before I RMA it (and waste another dose of thermal paste), I figured i'd see if anyone here has an idea of what's going on. Anyone have a clue, or is it definitely the CPU?

 

[Outlander_04]

disconnect the power and reset leads from the case to the mb
Now try and start the machine by momentarily shorting across the two power pins on the mb with the tip of a screwdriver

 

[breakingspell]

The motherboard doesn't seem to have a manual power switch, only a CMOS jumper. I can see how the front panel reset switch might play a role in this, so I booted with only the Power SW connector, and the issue still persists. It seems the most provoked to restart if I try to boot to any media, I can linger in the BIOS and boot menu indefinitely (although it has frozen on me twice in the BIOS). I've tried a combination of all USB 2.0 and 3.0 ports on the front and back, and i've tried to boot from a CD. I forgot to mention above, but I updated and downgraded the BIOS on the first motherboard. I haven't tried yet on this one, but it didn't make a difference on the first.

I recorded a video of the problem in action, I'll take care of cable management once i've got it up and running, hah. I did check to make sure none of the cables were coming into contact with the board or any other components, although I don't think this issue would be caused by a short.
https://www.dropbox.com/s/ol61ffoqowgtqsc/2015-04-20%2003.22.28.mp4?dl=0

 

[Outlander_04]

can you set an XMP profile on the RAM ?
at the lowest supported speed to start with

 

[breakingspell]

I was in the process of enabling XMP at 1600mhz, but the system rebooted while I was changing this setting. I Del'd it back into the BIOS and the system rebooted again after about 10 seconds. After that, it didn't reboot again, so I enabled Profile 1 and saved changes, the issue still persists 🙁

 

[Outlander_04]

then try disconnecting the front panel leads and starting it with a screwdriver as I initially said

 

[breakingspell]

Edit: I'm an idiot, I was looking for a dedicated pin/switch for power. Started the system using the Power_SW pins, and the issue still persists, just constant reboots.

 

[Dragos Manea]

Remove the ram stick one by one and boot your computer with just 1 ram stick, do this for both of ram sticks(boot computer with only one ram stick then boot only with the other one).

 

[breakingspell]

There's only 1 RAM stick altogether, and i've tried all four slots. I've even tested the memory itself in my desktop, works fine in there, as well as the HDD.

 

[Dragos Manea]

Well taking in consideration that u changed psu, rma the mobo, and tested hdd only thing that remains is either bios(try to update your bios) or the cpu.

 

[breakingspell]

It has to be the CPU, i've RMA'd the mobo already, and this one has the exact same issue. I'll go ahead and ship it off tomorrow, thanks for the suggestions!

 

[TofuLion]

not to get off topic, but i'm pretty sure the 5800K actually has better integrated graphics than the HD 6450.

 

[breakingspell]

It may, but the 6450 has 1GB dedicated VRAM, I didn't want to tax the 4GB of system RAM any more than I had to. The most intense game that i'll imagine will get played on it will be Solitaire, though, so it might be better to eschew the video card, i'll have to look into that.