Harddrive only running at 1.2MB/s specs included?

Checksum Error means you have a faulty memory module. It IS possible to buy a bad memory module. I bet what is happening is that you have either NOT populated the slots according to the motherboard manual instructions (typically, slots 1 & 3, skipping 2) or you have lost dual or tri channel speed + is that a Greenpower Western Digital? They are SLOWER, due to the supposed green power savings. If you have not retained dual or tri channel speed (depending on your memory configuration, motherboard) or you have one of the green power models, you will see a much slower computer. Checksum error always relates back to a BAD memory module that is producing the error. Check your motherboard manual and follow the instructions there. Make sure you populate the slots the right way.