itunes crash on vista!

[candy_poison]

hey to everyone.
I have a 3rd generation ipod, I use windows vista and everything was as good as it can be.
but one evening I opened up my computer, and 'as if by magic' itunes was not working.
not even opened.
when I tried to erase the whole program, I saw that there wasnt any itunes exe!
so it erased itself? or what. cos, I havent.
also I downloaded new version of itunes. And oops! it cannot be installed..
It must be about quicktime maybe...since it crashes all the time.
Now...
I cannot sync my ipod for 5 days...and helpless..
If anyone ever help, will be appreciated

thanks.