You probably need to give more details. If it's a replacement drive, did you reinstall Windows from a CD? Did you copy from the original hd? It's simple enough to remove the two cables from the original drive, physically remove and replace the drive, and hook up the new drive. But then you'd need to boot to a Windows CD in the CD/DVD player to format and install Windows, if that's what you're attempting to do.
There's possibly a recovery partition on the old drive )or a recovery CD). If so, you'd connect the new drive to a second power cable, and data cable (which might not be included in the tower) :
To restore system software from the Recovery discs:
1 Insert the Recovery disc #1 into the CD or DVD drive.
2 Restart the computer, then press and hold
R when prompted to display the restore process options. The
Options menu appears.
3 Select a restore process option:
- Press R to boot from the hard drive recovery partition
or CD. If no recovery partition is found, go to Step 4.
- Press F to format the hard drive and perform a full system
recovery, then go to Step 5.
4 Click a system restore option. For more information, see
"Restoration options" on page 5.
- Non-Destructive System Restore (Recommended)
- Full System Restore (Destructive)
- Full System Restore (with Backup) (Advanced Option)
5 Follow the on-screen instructions to complete the system
software restoration process.