They're probably already lost. What did you expect since you didn't back them up. You can try repairing windows, but youll probably need to reinstall. Either way you need windows 7 cd
http://logicalnode.com/temp/en_windows_7_home_premium_x86_dvd_x15-65732.iso Here you go. Just got it straight from the Microsoft website via MSDN.
I googled your problem: http://pcsupport.about.com/od/findbyerrormessage/a/bootmgr-is-missing.htm Restart by pressing Ctrl+Alt+Del