how do i get itunes to open on my computer? I clicked on the icon, but nothing pops up

I had downloaded iTunes a while back. Then something happened and I had to uninstall iTunes. I reinstalled iTunes a couple of days ago. It worked, I downloaded 4 songs and now, as of yesterday, iTunes will not open, launch or what have you. What could be the problem and how can I fix it. Also, trying to sync the 4 songs to my iPod, all of the songs I already had on there are gone, and those 4 new songs didnt even sync. ?????? Help please