If the make/models are the same you can try Acronis's premium cloning/imaging suite which comes free with any WD or Seagate HD in the mix, or free Macrium Reflect or Paragon 11 Backup.
WD Acronis free cloning app Seagate Acronis cloning free util Macrium - Image your system
You may have to boot the Repair CD to repair the boot sector to get it to start.
System Repair Disc - Create Startup Repair - Run 3 Separate Times
However Windows 7 won't start on dramatically different hardware without removing all drivers, hardware ID's and Activation using Paragon Adaptive Restore CD. You'll know if this is the failure because it will likely stall at the Windows 7 boot animation.
Again if the hardware is similar you can try making the Recovery Disks which should have been made when you set up each machine, then boot the ones from the good machine to reimage the new HD.
If these fail, you can order the Recov Disks for the new HD using theog's link, or find any retail Windows 7 installation DVD to unlock all versions if necessary and Clean Reinstall following these steps:
Reinstalling Windows 7