I think you're here because you can't solve steam_api.dll problem on your own, there are two kinds of solutions.
1.Click Computer on your desktable and right click Disk C to select Properties.
2.Click Disk Cleanup, you'll see a window just as right, this process need some minutes.
3.Under Disk Cleanup there are Files to delete, tick the files you don't need to free pc space, finally click OK.
1.Step by step click Start>Computer>Properties.
2.On the left pane Click on System protection.
3.Go to System Protection and click System Restore, then OK.