I got a Dell Inspiron 6400 from someone I know - it's basically having overheating issues.
I suffer severe performance decreases (stock CPU speed is 1.5GHz - it dials down to 1GHz) because the BIOS is downclocking the CPU to prevent it from frying.
It's a mobile Core 2 Duo processor, and I'm looking to fix it up so I can use it as my own.
From what I can tell, the overheating is due to the single fan in the laptop not working. It's supposed to start spinning when it starts heating up, but it doesn't spin. I took the thing apart and tried starting up the PC with all the covers and whatnot off to see if the fan spins on (like a desktop PC's fan does when it turns on goes through POST) but it doesn't spin. Of course, if I put it back together and turn it on, it's hard to tell if it's spinning. I basically poke a needle through the grill on the bottom and try to see if the plastic fan hits the needle, but from what I can tell, the fan simply isn't spinning while the computer's on.
I tried replacing the fan with a known good one - that didn't work, the fan still doesn't spin. I tried reapplying thermal paste just to make sure - that didn't work either, though I do get a few degrees cooler temps now.
The next thing I tried was running Prime95 to force the CPU to heat up to try to get the fan to kick in. The fan doesn't spin (I tested with the needle physically to see if it's spinning); the CPU ends up downclocking instead. I also installed SpeedFan - SpeedFan doesn't detect ANY fans, period.
From all this troubleshooting, I'm thinking it's a motherboard issue, but I just want to make sure in case I'm overlooking something blatantly obvious.
As a heads up, this laptop is about five years old and is well over warranty, so I can't exactly go to Dell support for help - I don't want to waste $100-$200 just for the call, as that is already beyond the worth of this laptop.