Steam_API.dll is a dll file used by the “Steam” application which connects your games with the application. The games that frequently crash due to the Steam_API.dll error are Call Of Duty Modern Warfare 2, Just Cause 2 etc.
Sometimes it is necessary to register DLL files to make an application o service work again in Windows 8.
A Windows 7 feature that is disabled by default is “Concurrent remote desktop sessions”. Basically, a concurrent remote desktop session allows several user to connect to a system trough the remote desktop feature, so multiple user can access and control your system.
Are you trying to play any games that require Microsoft Live? Games for Windows Live is a pretty cool service, but it can also cause a lot of trouble. Sometimes Windows 7 and Vista will give you some weird errors, e.g. that xinput1_3.dll or xlive.dll is missing.
This is a description what you can do to fix the problem.