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?
Did you completely wipe the hard drive before reinstalling? Could you have a boot sector virus?
If you have it, boot from Dell Resources CD and run the extendedhard drive tests to see if your drive is failing. Or read this <ADMIN NOTE: Broken link has been removed from this post by Dell> about creating your own bootable CD with the hard drive tests on it.