Question About Upgrading Video Card Heatsink

[Typ0]

I found a really strange issue when I tried to change out the heatsink on my 8600gt to a Zalman VF-900. When I swapped out the heatsink I kept getting a video Post error. I doubled checked the thermal paste and mounting of the heatsink. I looked at the base of the zalman and the paste was spread out evenly and thinly (I could see the nvidia logo pressed into the thermal paste).

When I changed back to the original heatsink, the computer booted up normally. Is it possible that the video card actually detects the presence of the fan (resistance or some kind of load sensor) through the 2-pin connector?

Has anyone ever experienced this kind of issue before?

[Lsdmeasap]

Did you check to be sure the heatsink screws are not shorting the card out somewhere?