cold startup / sys fan

I need to find the answer to this problem too!  If left off for several hours and then turned on, my inspiron 6400 will take up to 30mins to boot up and the fan remains on the whole time.  I then turn it off and when I turn it back on a minute later it works fine.  The crazy thing is if it is turned off and then turned back on within a certain time frame (maybe up to an hour or so) it will also work fine.  I got a replacement system thinking it sounded like faulty hardware but the problem remains in this new computer.  I also thought it could be the cold weather we are having.  Could it be low voltage in my house, an initial search for my wireless network after a certain amount of off time (does my modem need reconfiguring), or my computer installing upgrades it downloaded the night before??

Hi, I've had the exact same problem with my 6400. The problem only occurred on a cold boot. I managed to get into the dell diagnostics when this occurred and I ran tests on the thermal sensors. They all failed - the sensor readings were actually out of range, the readings suggested that the CPU/graphics chip temperatures were at 255 degrees celsius. Thinking the system was overheating, the fan was on all the time and the CPU was severely clocked down and its L2 cache was also disabled (the CPU test showed L2 cache failure). This explains the slowness of the computer. I've since got two more replacements (the fan on the second one was OK but it had other issues), and the latest replacement I got seems to have the fan problem again although it is more intermittent (not showing up on every cold boot). I think this fan issue may be a common problem among the 6400s, and I believe that the reason not many people have reported it thus far is because it most likely shows up intermittently, and many people probably aren't aware of it and thinking it may be due to some problems with Windows.

In any case I'd like to hear from anyone out there who's had the same problems and see how widely spread this issue really is.

I also have this problem. The diagnostics doesn't find anything wrong with my system. It often happens on resume, and even after restarting it still happens, during the boot up (almost immediately) onwards.