Can't open itunes on computer

Last week an update showed on my computer for itunes. I selected to install the update. As far as I can tell it updated without error. Since then I have not been able to open itunes. I get an error message saying itunes in not installed properly and to reinstall itunes. I have not hooked my ipod to the computer in 2 weeks and it is working fine. How do I reinstall itunes and will I loose the itunes library that I have?