You have an optimus setup ?
There's a few ways to help this problem. I think Boris recommends using the Injector version of ENB instead of the wrapper version.
Only thing with that is you need to start the injector first before the game.
The best solution I found for my eldests laptop using the wrapper version is :
First go to NVidia Control panel ( right click desktop )
Manage 3D Settings
Click on the Program Settings tab if it is not already selected. ( You can do this on the Global tab aswell if you want to use your NVidia for everything )
Select Elder Scrolls V: Skyrim ( Tesv.exe )
"Preferred graphics processor", change this drop down selector to read "High Performance NVIDIA Processor". Then Apply your settings.
Also do the same for the launcher :
Next to where you selected Skyrim, there's an Add button,
Add SkyrimLauncher.exe ( you will need to browse to steam \ steamapps \ common \ skyrim \ .. to select it )
"Preferred graphics processor", change this drop down selector to read "High Performance NVIDIA Processor". Then Apply your settings.
( The reason you want the launcher enabled aswell is when it tries to detect optimal game settings to be using the NVidia hardware at the time )
Now follow the instructions to use NVIDIA OPTIMUS D3D9 DLL FIX - http://www.nexusmods.com/skyrim/mods/33227/?
It chain loads the enb .dll when you rename the enb dll as d3d9Orig.dll
It works a treat
Dont forget to delete your old skyrimprefs.ini and skyrim.ini ( my documents \ my games \ skyrim \ ) - Now that you are setup for the correct graphic card selection by the launcher and the game, you need the game to recalculate your optimal game settings .. After deleting them, just launch skyrim launcher and it will auto generate new ini's.
Edit: One thing to watch out for - When you update nvidia drivers, if you choose Clean install, those profiles you just created will be deleted so you need to do the nvidia conrol panel bit again .. Or just dont use the driver clean install option.