Some users have reported an issue in which iTunes 10.1 for Windows installs properly but will not open. In many cases, this issue is due to a problem with the Bonjour service installed in conjunction with iTunes, and can be solved via one of the following routines:
Check Firewall settings. Follow the instructions in this knowledge base article to unblock the port used by Bonjour.
Uninstall then reinstall Bonjour. Some users must completely remove then reinstall Bonjour to resolve this issue. Follow these instructions to do so.