Overheating MB When Running Handbrake

I built a quad core system last June '08 using Intel's DG33TLM motherboard. Everything has been working fine until last week when I was trying to encode some video for my iPhone. I have been using Handbrake which was working great. In the past, I have noticed that Handbrake uses most of the CPU resources and cpu utilization is close to 100% for all 4 cores. Last Thursday, my system started shutting down due to overheating when running Handbrake. This happened under both Windows 7 beta and Vista Ultimate. When I am not running Handbrake, everything is fine. Does anyone know what is going on? Thanks in advance for your help.

I assume you are using the stock heatsink. Check your idle and Prime95 small FFT temps with Core Temp.

You probably have a loose HS, check the mounting pins. They may not be fully seated even though they look like they are.

Or better yet, get a XIGMATEK HDT-S1283 120mm Rifle CPU Cooler with the XIGMATEK ACK-I7751 Retention Bracket. Check the case width for clearance first.

When applying thermal paste with the Xigmatek cooler, apply a thin layer across the CPU IHS (top) or across the whole base of the heatsink. The paste won't spread properly through contact because of the gaps between the heatpipes and the base.

"There is also an option in Handbrake when using the h.264 Codec, you can go to the Advanced tab and add :threads=1 to the end of the string. This forces handbrake to only use one thread and reduces the CPU usage."

I am very new & unfamiliar with Handbrake. It's my first time using it as a matter of fact. I also have the CPU Usage problem & would like to try your suggestion. But I need you to guide/walk me through your entire suggestion.

Please be as detailed as possible.

Thank you