Part of screen went black after iTunes update and playing video games, After

Ok guys never had this problem before but part of my iMac's screen went black and the black parts were moving around, again I never had this problem before and it happened shortly after I installed the iTunes update and while I was playing Plants vs. Zombies. I had to hold the button to restart and decided to use time machine to go back to a previous version, it's been a few days and it hasn't done it yet, but I am freaking out because I don't have the money to replace this for the next few months, should I worry, any suggestions on what to do and have anyone else gone through this? 😕

Thanks,

Mayhone!

anyone have this happen, please I still need some input...