M15x

There can be multiple reasons like heat throttling (cooling vents all clean?) or too many things happening at the same time (You checked for malware?).

Turn the graphics card back on with the button near your alien sense

Too many running applications on background?
Check your temps, it could be an overheating...

Another reason could be the settings you're using.
You have GTX 260M right ? if so,then it can't max out games on resolutions like 1080p,lower your resolution and check if it makes any changes or not