Game Screen gets stuck while everything else is running

I'm sorry if this comes off wrong and but right now I'm very frustrated!!! First game everything was going fine and my team was winning and suddenly as i jumped in to a fight my screen froze. I can hear some game sounds in the background but the screen was completely stuck. I couldn't even alt+tab out. It was stuck in the fracking game screen. I had to go to the task manager and exit LOL and load back on. I thought it was a one time thing. Then second game it happened again!! We were winning and screen got stuck. The only things I had running in the background was skype. I switched off everything else. Please let me know why this is happening. Is this a unique problem for me or is it happening everywhere? It's extremely frustrating when you lag out for no reason during a winning game and the other team wins and mocks your team. Thank you!