Since you replaced the HDD with a new one, then your NEW hard disk drive must be detected and initialized by your system without any problem as long as it is connected to the motherboard properly.
Now, since the NEW disk is blank, you need to INSTALL Windows on it to make your computer usable.
This requires a working Windows installation DVD which you mentioned, you already have and it is a Windows 7.
Now, when the computer boots, it normally boots to the HDD. Since the disk is blank, hence you get the error. To fix this error and make your computer usable, you need to set the computer to FIRST boot into the CD/DVD drive so that the installation of Windows 7 will start. This is also why I asked you if the Windows 7 disc is indeed an installer or not. If it is an installer, and your system was set to boot from the DVD, then installation of Windows 7 should start. If it is NOT an installer, even though your system is set to boot from the DVD drive, no installation occurs and you will be getting the error that you have been getting.
Please check and let me know your results so that I can assist you further.