iTunes wouln't start...

For the last two days, iTunes would not start. (iTunes has encountered a problem and needs to close. We are sorry for the inconvenience.)

-- Searched desperately, the Apple site, uninstalled the software (including removing any trace of the old install), restored the system to several older dates, to no avail.

Cannot think of what could have caused this.

Any tips or advice?? -- I run XP, all up to date.

thanks a lot,

Mandel