itunes will not launch after upgrading to 11.1.5 with my 10.6.8 mac book pro

as soon as I upgraded to the new itunes, when clicking on the icon in the dock I noticed the icon bounced up and down once but itunes never opened up. Tried it latter in the day and it still would not open. My operating system is 10.6.8and I have the current apple updates installed up to this date today. the funny thing is I waited on the itunes update, and then decided to go ahaead and upgrade and soon as I did, well you know what happened. If I could ask a second question, what if I just went back to the original software version when I bought this computer, would I have less problems. I tried this earlier because of problems with flash and my nikon software needed the apple upgrades to work (they no longer make the older version). BUt when I worked it on the original software everything worked great (no nikon) but I could not see the videos on youtube, and other internet content on various sites. So my question is, if I decide to cut and run back to my old home, how could I solve the the flash problem or could I just get an earlier version of flash? My mac book pro I beleive came with 10.6.4, or what ever they had about three years ago around November. But this itunes thing is really bothering me and if I can fix this then I will avoid any further iupgrades even if someone puts a gun to my head. Just kidding. Thank you again for your help