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Motherboard fails to post BIOS: CPU Fan spins but no video or system boot.

copeasetic asked
System Integration Problem

Mainboard: Asus P5B-MX
Memory: 2x 1GB Kingston KVR800D2N5K2/2G
CPU: Intel Core2 Duo E6550, JGA775 2.33 Ghz, 4MB L2 Cache, 1333 Mhz FSB
Power Supply: Thermaltake TR2 RX-450 ATX 12V 2.2 (TR2 RX-450PP)
 Modular cabling power supply
Hard Drive: Seagate Baracuda 7200.10 320GB
Chassis: LianLi PC-A01

I am a system integrator and I am building a client a small footprint workstation with the above hardware configuration.

I have been unable to get the mainboard to post.
 - The board's power indicatior lights up when the P/S is plugged in, but not initiated (the power swith on the p/s is switched on, but the mainboard power not initiated).
 - When engaging the chasis's power switch the CPU fan starts spining, but no video or system response.
 - I have tried this with the 12v power cable unplugged as well and the fan still spins, still no post.
 - Same condition occurs when I jumper the pwrsw with a screw driver without chassis power switches plugged into the mainboard.
 - The board does not report any error codes (no beeps from system speaker)
 - Same condition occurs when CPU, Memory are the only components installed.
 - When I plug-in one of the modular power cables into the power supply and connect the hard drive power the CPU fan will not spin up when the power is engaged.
 - Monitor is functional.  

Troubleshooting efforts:
 - Removed the board from the chassis to troubleshoot the possiblity of a short.
 -No effect
 - Swapped Power Supply (Antect 450W Smart Power ATX v2.0)
 - No effect
 - Tested the old Powersupply on another system and it powered up just fine.

 - Swapped out the motherboard
 - Swapped out the CPU
 - Pulled the memory
 - Tried 1 stick of memory at a time (no error reports at all)
 - Installed video card in PCI-E slot (no change)

I am at a loss here. I am going to test the CPU in another machine today, but I find it unlikely two CPUs would be bad.

Any thoughts?
Thanks in advance!
Watch Question

Check RAM is on the Mainboard Qualified Vendor List. I have had similar problems although the CPU fan not spinning up when HDD power connected is a strange one on me.


I have double checked the memory QVL and determined the memory I have installed is not on the list. I have ordered new memory and will post my results once I get it installed.
Distinguished Expert 2019

you connected the aux 12V power connector ?


In response to nobus -

Yes, I have connected both the main ATX 24 pin power connector as well as the 4 pin 12v CPU power adapter. I have tried this with two separate power supplies as well as on another ATX systems which did power up.
Distinguished Expert 2019

since you swapped everything, i suspect you either made somewhere a mistake, or have more than 1 problem. that is, if the new memory does not help you farther


Here's an update:

I swapped out the chassis, changed the mother board to: P5KPL-VM and used QVL memory. I tried the CPU, memory and power supply on an ATX system and they all checked out. The only thing I can think of is the chassis is not designed to run this combo of components. I am using the LIAN LI PC-A01. It says it is ATX 2.0 compatible. The motherboard is a MicroATX...

The system just will not boot. The CPU spins for 1 second and stops. Same issue as before.

This is maddening.


I just determined that the hard drive has been the cause of the failure. Can someone tell my why a hard drive would prevent a machine from powering up?
Distinguished Expert 2019
it can easily, since it is connected to the disk controller interface, in fact, all device can lock up a pc
in fact, i made a mistake : "since you swapped everything"   --> you did not apparently; sorry for that...
Sorry - been away.
That's the great thing about PCs anything can cause just about any problem!
I once had a network card that when used with a particular mainboard caused the floppy drive to fail formatting floppies at 99% and I swapped out all parts in that PC twice over before determining the problem!
Glad to hear you sorted it in the end.

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