Startup issue

[Moo]

So i just built a new computer. I plugged everything and started it but when it was booting up it could not read the disk and the keyboard was not working. Both are definitely plugged in right and i know they are both compatible. When i plugged everything in though i realized had also plugged in a hard drive from one of my old computers. I think i remember seeing somewhere that this could cause a problem. What should i do?

 

[Moo]

its an abit 939 dual-sata2 if that helps at all

 

[Moo]

ok so i decided to see if i could do anything to change this and eventually tried taking out 1 (of 2) pieces of ram. I did, booted up with hard drive and it seemed to be working but said windows wouldnt load. it gave me options i could do and i chose start windows normally but it then took me to the boot menu. I put the boot up on the hard drive but it wasnt reading it for some reason. i rebooted and the same error i started with happened, back to square 1. Really random stuff

 

[jeremy]

what do you mean by
"I put the boot up on the hard drive but it wasnt reading it for some reason"
"windows wouldnt load"?
give more details,be more specific