Dude, you do know Warcraft III does not support NT. In other words untill you get a new operating system you can't play wc3
Then you got lucky that time. I am not really sure how it can be fixed, but I know that warcraft III has a lot of problems on vista, you should google it and see what comes up.
Did you by any chance install a new vista since your last wc3?
Also can you make a list of tehnical software you installed since then(such as .NET framework, msxml, dxc and similar)
Try running in compatibility mode. A friend of mine had to run WC3 in Windows 2000 compatibility mode just to make it run. Getting Vista was not a smart choice.