Since you can't boot into Windows, you’ll need a Windows 7 installation DVD or a bootable USB drive.
Remove any non-bootable USB drives or external hard disks. Your PC might be trying to "boot" from a thumb drive that doesn't have an OS on it. windows 7 bootmgr download
, which contains the necessary tools to automatically recreate or repair the file for you. Super User How to Fix a Missing BOOTMGR If you don't have your original disc, you can download a Windows 7 Disc Image (ISO) Since you can't boot into Windows, you’ll need
If you have a non-bootable USB flash drive or external hard drive plugged in, your BIOS might be trying to boot from it. Unplug everything and restart. , which contains the necessary tools to automatically
: You can find archived versions of the official Windows 7 Repair Disc (x64) which contains only the recovery tools, not the full OS. Fixing the Error (Step-by-Step)