Hi,
I would suggest you to follow the steps and check if it helps.
Method 1: Perform a clean boot and check if it helps.
**How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7**
NOTE: Make sure that you perform “step 7” in the link above to boot your computer normally.
Method 2: Install itunes in evaluated mode by following the steps and check if it helps.
a) Right click on the file or program you want to run as administrator.
b) Click on Run as Administrator.
Method 3: You may also follow the steps in the link and check if it helps.
Trouble installing iTunes or QuickTime for Windows
If the issue still persists, contact Apple support for better assistance to resolve the issue related to installing Itunes.