Strange Overheating Problem

I have a strange overheating problem with my CPU. Whenever the case is upright (designed to be standing), the CPU will overheat and the machine will shutdown. However, when the the case is laying flat, I do not get the overheating problem. I tried removing the side panels while the case is upright, but it still over heats. However, while laying on its side with or without the case side panels, the overheating problem does not show up. Is there something I need to check as to why it is overheating when the case is in the upright position. This machine is used as my Snapstream Beyond TV Server for recording TV.

Hardware
Old Case
Abit Av8
XP X2 4400+
MASSCOOL 5T568S1H3 Heatsink
1 x 80 WD
1 x 1.5 WD
2 x PVR-150
Crosair 650 PSU
1 x intake fan
1 x outlet fan

Thanks

Is it possible that the air is getting trapped at the top of the case, but getting out of the side when you have the case sideways?

Does it overheat if you place it upright in the middle of the room, that is, with the case being able to properly get rid of the heat?

maybe a low pressure mount with your heatsink and cpu and turning on its side moves it some, what is the mounting like with that heatsink?

Dragon

Sydney,

Yes, even when I have the case in the middle of the room or rather the case turned toward the middle of the room with the side panel open, yes, it will overheat and shutdown. However, no matter where the case is with or without the side panels, when laying flat, the overheating issues is gone.

Dukemurmur,

The heatsink is mounted using the standard 939 brackets on the MB. When trying to wiggle the heatsink, I get little to no movement at all. However, I was thinking about re-seating the HS, however I'll have to wait until tomorrow to get my Artic Silver from my friend. I did not think this was it because I just set the HS over the summer, and it has not been overheating until recently.

From what you're describing gravity has to be playing a role somewhere. Whether it's the heatsink being loose and shifting, an old fan getting stuck, or a loose cable getting tangled in a fan (stopping it from turning) it's obviously positional ...