After the machine is assembled, you turn it on. Since it has no OS, it will boot to the BIOS. Make the drive mode selection, (the "integrated peripherals" section of BIOS is where you'll find the drive mode setting), put the Windows disc in the DVD drive, then reboot.
You navigate BIOS using the arrow keys, enter, and escape keys.
More important than this, (and before turning it on), is double checking that the RAM is properly seated, >>the end locks in place in the notches, the PSU wiring done correctly, and the CPU heat sink being seated properly. In other words, did you hear a click from each pin as you pushed it in?
The video card also has a retaining clip on it make sure the card is seated properly, and the clip is in the notch.
btw i allready installed the OS on my new hard drive from my old pc i sold to my dad, will this make a difference ?
I put it on incase i had problems installing it at the last minute ?
OK that's dumb. The OS detects each piece of hardware, and adjusts itself accordingly. So, what you have is, an OS install that still thinks it's in your father's computer.
Earlier in this thread you were told about this, I guess you just chose not to listen.