CPU running at 100% after memory upgrade

This question first originated here: https://www.experts-exchange.com/questions/29053053/CPU-running-at-100-after-memory-upgrade.html

All the HW details can be found there.
I had used CL5 RAM on a motherboard that took CL6 RAM. We assumed the processor was doing 100% because of this, and that it couldn't handle the full 8 GB that the mainboard was supposed to be able to take.

So I bought new 8 G B of memory, this time CL6 from here: https://www.ebay.com/itm/For-Kingston-8GB-PC2-6400-4-x-2GB-Desktop-Memory-DDR2-800Mhz-240pin-CL6-DIMM-RAM/222696177816?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

But I still have the same problem. When all 8GB are installed, the CPU goes up to 100%, when I remove one memory stick and am left with 6 GB the CPU operates normally. Suggestions?

Makes me wonder if something is broken in the motherboard.

With all together 8GB of CL5 ram (see the first link) + 2 x 1 GB of the same RAM from before and now 8 GB of CL 6 RAM (all together 18 GB), I wonder what I am going to do with all that RAM that I apparently can't use. I will have to look for motherboards that can take these memory specs. Any suggestions?
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RaminTechnical AdvisorCommented:
Did you check if there is an update for BIOS / Chipset driver ?

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David Johnson, CD, MVPOwnerCommented:
if you open task manager what process is using the most cpu?  BTW DDR2-800 memory runs at 400mhz but runs at double the clock speed

In addition to double pumping the data bus as in DDR SDRAM (transferring data on the rising and falling edges of the bus clock signal), DDR2 allows higher bus speed and requires lower power by running the internal clock at half the speed of the data bus. The two factors combine to produce a total of four data transfers per internal clock cycle.
did you try the 6 Gb setup by removing stick, then 2, , 3 and 4 ?  and all run ok ?
itniflAuthor Commented:
Upgrading the BIOS actually fixed the problem. Still using the CL6 memory bought on ebay, not tried the CL5 memory that showed the same problem when the full amount of 8 GB was in use. Hoping the performance won't be too different.
RaminTechnical AdvisorCommented:
Thanks for the feedback.
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