Motion interpolation HDTV connected to a PC

I have had my "240hz" HDTV for a while now and I feel like it doesnt work as well as it used to, now I dunno if its just cuz I got used to it but I do not get the "fake" feeling anymore as if stuff is sped up.

Now I heard people say the interpolation effect gets turned of when the HDTV detects a PC cuz of games, but seeing as it used to work I dunno why it wouldnt now. Is this a real thing, do I need to do something to have it work with PC ?

While on the subject, would a PC driven Motion Interpolation effect be anymore powerful then the one my HDTV is providing ? If so any tips on a guide, found a few but they seem a bit outdated.

I often swap between my LCD and HDTV via the Nvidia panel, LCD on DVI and HDTV on HDMI.