None of my games are playing anymore. Granted there are a few games on my computer on s...

None of my games are playing anymore. Granted there are a few games on my computer on steam that are playing, but a mass majority of them are not playing and I have no idea why.. I haven't done anything different lately. Aside from not playing steam for about *-* months. I have made sure everything is up to date, GPU, windows, the works. **I have also made sure that all the games are on the acceptance list of my antivirus.. they wouldnt not be on there tho.. as I have played all of my games before this.. But again for some reason none of my games will play or even correctly download. When I launch a game merely * seconds later the game says syncing then nothing. In some cases the game will open but wont go any further than that.