My computer will not boot up correctly?

i have i acer aspire 3680 and it had vista on it i desided i wanted to upgrade to windows 7 and it worked but it was on a different portion then vista so i then i deleted the windows file on the d drive (the one that ran vista) the i restarted the computer now it says that i am missing the ntldr press ctrl alt delete to restart??? how do i fix this pleaseeeee help