Why does my nikon D3100 stop recording video?

I Got a NIkon D3100 a few days ago and today i tested out the video function. The first thing I did with it the entire day was record a 30sec clip in 1080. Then i attempted to take a longer video also at 1080 but it cut me off at 3min 29 sec. Each video i tried to take after that would auto stop after a shorter and shorter period of time. The ambient temp is around 60F and my battery is/was fully charged… I'm using a 8GB PNY class 4 SD card with 87 other pictures on it… Any idea what's wrong?

Internal heat is he problem. HD video produces a very large data flow that heats up the parts of the camera it passes through. The hotter the inside the shorter the video until you have to let the camera cool off.

The problem with dSLR the same with compact camera video, you can only record a certain length at a time. That length has a maximum but the minimum depends on the data transfer rate. For video a class 6 or higher is best for a dSLR. I use a San-Disk Ultra II for my video and I get the full 5 minutes of HD video the D300s can handle at a time.