this is indeed a virus.
to get rid of it, you will need to install and update an anti-virus.
i think this will not be possible in your case since the computer is not allowing you to do anything.
so, try to enter the safe mode.
to do this, press F8 repeatedly when booting your computer, before the windows logo appears.
then you may do a system restore to set your computer to the settings to a date when these problems were not yet encountered. that is the date before you downloaded the iTunes.
this should make it work normally.
after the system restore, you may download the AVG free version anti-virus, or you may buy the full version.