If you can't get a picture up on the screen at any point (i.e. the TFT LED never turns green), then this won't be a driver issue.
You didn't say just how old the computer actually is but I guess it's possible that if it's really old (or more to the point, the video card is really old) then it simply may not be capable of running the TFT. Another possibility (although this is a long shot) is the TFT cable. Obviously the cable works as the monitor works with other computers, but it may be just too long, or too poorer quality to work with this particular computer.
One more thing - you said the computer was working with a CRT monitor originally, but have you actually tested the computer on a CRT monitor since you've had this problem with the TFT? If not, then it could be that something else is wrong and has nothing to do with the TFT monitor at all.
Edited by Samm, 24 January 2008 - 04:45 PM.