I have a Optiplex 745 that when I turn it on, it says that the Bootmgr is missing and to press Ctrl, Alt, Delete to restart. I restart and it still says the same thing. My hard drive is first in the boot order priority. I ran a BIOS diagnostic and it passed. I have a Windows 7 install disk and it seems to work but halfway through the install I got a blue screen (IRQL not less or equal). How can I get this "bootmgr" back?