I just had that freaky "NTLDR is missing". I have a multi-boot system with XP pro, Vista and Win7, on a 320GB hdd with all my work.
This happened after I did the latest update for Win 7 -just a few hours earlier.
Here's what worked for me:
Partial solution: I pressed F8 during bios screens and when BIOS boot selection menu appeared, I selected (with up/down arrows) the main hard drive and was able to enter the multi-boot menu and start the OS I wanted normally. But when I rebooted, I got
the same error.
Since the above worked, I figured out it was definitely some sort of BIOS corruption.
So...Full solution: I noted on paper all BIOS settings, then updated the BIOS (with the same version since there wasn't a new one), then re-entered the BIOS and selected BIOS defaults. Then changed each setting back according to the notes on paper with
the exception of letting "PCIPnP" (Plug & Play O/S) to NO. Before I reset the BIOS to default settings, I tried again and I got the error message. So what actually fixed it, was the reset of the BIOS settings to default -try that before re-flashing the BIOS.