Question ram not working properly with 64bit windows 7 or 10

[jairustoney50]

so i bought two 2gb stick of 800mhz ram for my computer but every time i try to boot into windows 10 or 7 64bit the cpu stays at 100% usage making it unusable,but when i boot into windows 32bit it works normally but only usase 3.5gb of ram and when i boot into windows 64bit with only 3gb of ram it also works normally and when i look in the bios it shows 800mhz speed but when i boot into windows i see the ram is capped at 400mhz per stick how do i fix my os or bios
cpu pentium d 925 3Ghz,4Gb DDR2 PC2-6400,chipset-ati Xpress 1250,LGA socket 775,motherboard-i cant find the model number because is says to be filled by o.e.m but the manufactoror is parckard bell bv,and this model is called berkeley i hope i can get help with this

 

[Plicker19]

Your computer might have a maximum of 3gb RAM. look up how much ram your PC can support.

 

[lynx1021]

That is a old computer, maybe around 2009. My 2009 Modified Dell server power edge SC430 with a Pentium D 925 CPU 3.4GHZ is running windows 7 pro 64Bit with 4GB memory, max for that model. Need to Know what the serial number is or the number off the Motherboard like "MS-7104" to be able to help. How are you changing operating systems to try? You can't just take a hard drive out of another computer and expect it to work. You have to load the operating system on the hard drive that is on the same motherboard. I believe MSI made most of their motherboards.