NTLDR is missing message comes from the OS itself, so this means it can see the disk. This message means that the BIOS did the hand-off to the disk, read the boot .ini and found where the OS is, but the path did not resolve. So the first thing to do is to check the boot .ini and see what is in there.
One example of a situation where a BIOS update can cause this is if the OS volume where Windows is located had its drive letter change. Such as if you are using multiple hard disk and Windows is in D: a BIOS change could cause the re-enumeration of volumes and D: is now E:, etc. If it is a situation where your OS was on C: but now that volume is a different letter, then it may be better off reverting that BIOS version again as the Windows installation could have problems with the drive letter changing.
NOTE: The forum will not let you type in the term I put in bold above without a space. You will get an error if you try to submit a post without the space.
EDIT: I'd also like to report that while the retroweb (site linked earlier) is good for information, I find their software to be lacking. That site does not take into account board revisions such as is common with Microstar boards which means this issue will likely exist for other brands. That would be a reason why a BIOS update may fail. Also I've yet to find any drivers on there that have worked. For example, ones that are marked for Windows 95 requiring different OS like XP, or 32bit options are 64bit versions, etc.