I’ve got a stock Dell Dimension E510, and lately my CPU fan has been revving up a bit while I’m working/playing on the computer, just every once in a while, for maybe 20-30 seconds or so to mid or mid/high speed. It never used to do that, the fan barely ever broke idle, but I figured the vents and heatsink were getting clogged up with dust and things were warming up in the case so it had to run a little higher on occasion to cool down a bit. I bought some new ram (same specs as original memory, just bigger cards) to upgrade the memory, from 1GB to 4GB so while I was putting that in yesterday I cleaned out the case, the fan, vents, took the heatsink off the processor, cleaned that up good, and there was quite a bit of dust clogging the vents and heatsink. I put it all back together, started it up, it recognized the memory change just fine but shortly after, the fan started revving up higher than I’ve ever heard it, the thing had to be maxed out. So now any time I have any application, program, or even a browser window running the thing just takes off. If I close all open programs and let it just sit, it’ll eventually slow back down to idle, but shortly after, start revving up again even though my CPU usage is between 0%-3%. I let it run for awhile thinking for some reason the processor was getting really hot, but I shut it down, took it apart, felt the processor and everything else that produces heat and everything was barely above room temperature, so nothing is overheating, but the fan runs really high anyway. I tried putting the original memory back in thinking maybe that had something to do with it, but that didn’t fix it. I’ve checked settings but unfortunately I’m not finding any fan speed controls. I've been running the latest bios for quite a while so I doubt it's that. Is there a temp sensor somewhere that is all screwed up? I’m not really sure what to do at this point, any ideas?