I just started the Witcher and really like the game.
However the audio in the cutscenes sounds great, but the video is not in sync. After the sentence stops, cutscenes just go on for half a minute or so. Very annoying.
Also cursor in menus starts great but if reopened is delayed. Almost as if there is not enough speed in the system.
But the pc is only a few months old, so almost empty.
i5 processor working on Windows 8.1, 3.2 Ghz cpu speed and 4 gb ram memory (not the best, but not too bad either).

Any suggestions to solve this?

Seems like an FPS problem, you didn't point out a GPU, if you're playing with the onboard GPU (CPU), that explains your problems.

4GB of RAM is also not good for gaming nowadays, I don't know how much RAM this game uses on Low Settings, but can go over 5GB on High Settings.

Make sure you have a GPU (Graphics Card) and it's proper drivers, your lack of proper RAM also takes it's tax.

The i5 alone can't run this game!