Something is wrong with your system. Based on what you describe I wouldn't assume Steam is the problem. After all Steam is only launching a game, it's not running it, your system is. And if a game won't run, could be a problem with the game. If no games run, then sounds like an issue with your system.

So... what are your system specs?

Have you made any changes recently? Upgrades, updates, etc? Anything weird happen lately? Have you moved the system recently and maybe plugged your monitor into the onboard video and not your dedicated GPU? (People do this sometimes absent mindedly)