Why does itunes keep on crashing??

Itunes repeatedly crashes, I have windows vista and an ipod touch.
For example i just cancelled a sync it then froze so I closed it successfully.
I then tried to reopen it but when i clicked on the icon it loaded but did not open.
I then logged off my user name and logged back on but it is now saying
' I cannot open the application Itunes because another user has it open' but I am the only user which uses itunes.'

It is very annoying it crashes often, and some of the songs on my ipod are distorted and I am wondering if it is because of itunes as it is only after I have synced my ipod they become distorted.

I would really appreciate it if someone could tell me why this is happening