1st solution try system restore if still doesn't work
2nd unistall that shity vista skin and reinstall nero and that Jdownloader if still doesn't work
last and best solution for you install fresh windows xp without any crapy vista skins.
Remember these vista skins aren't proper codded and sometime makes your system unstabile and some programs wont work.If you are that bored of windows xp install real win vista and enjoy because your pc alredy works slow with these skins and you cant see big difference.