inaccessible boot

Everything was working fine until I was trying to upgrade RAM but realized the upgrades I got was not compatible with the motherboard that I have. so I reinstalled the old ram and it started giving me the "Inaccessable boot device" stop code. I remember where it started happening was when I was...

Hello, i would like to know what people mean when they say , its a good processor but it has weak cores, is it just the ghz or there is more? tell me everything please