What is the reason my computer is showing that the NTLDR is missing

sometimes there are many things that can cause this to happen. the os could have just naturally messed up. there could be a program that caused this or any other number of actions. the way to repair this is to have a repair media available or the original install disk and start the computer from there and have it repair the os or you can copy the ntldr from the media to the correct folder on your computer. I hope that this helps some and your computer is working again soon