"ntdlr is missing" and "couldn't open boot pa

I just assembled a computer which I bought in parts from tiger direct.....I put in my windows 2000 disk, it goes through the whole thing to where it normally will restart to continue installation I believe (it says it's booting windows or something to that affect)...it then loads a "STOP:" screen....every time it's done this the error has been different....IRQL NOT LESS THAN OR EQUAL was the first.....I then have to shut the computer off (by shutting it off using power switch in back because that's all that will work)....when I restart (CD still in drive) it doesn't take me back to installation but instead to a screen that says "NTDLR is missing, press ctrl+alt+del to restart".....no matter how many times I restart it goes to that.....thinking it might be an issue with that particular harddrive, I put in another (same brand and size) and repeated my steps and the exact same thing happened (diff error message this time however, but still a BSOD with the STOP: error message just a diff one). Getting frustrated, I left it for 24 hours. I come back, boot up, and it goes back to installation disk again. I try again. Same thing happens for a third time. What kinds of possibilities are we talking here? Could it be something as simple as a jumper adjustment? Or are we looking at something more major? The only hardware hooked up it the dvd-rom/burner/cd-rom/burner and the harddrive....all other components are a part of the mobo. Someone please help me before I lose my sanity!! Thanks and sorry for the long post.