I have noticed a marked 'slowing down' of my PC recently with the hard drive activity indicator light seemingly permanently lit as if it is constantly processing data or whatever. I had thought it was a rootkit infection (separate thread) but no malware has been picked up by the numerous scans I have carried out. What I have noticed is that the fan in the PC tower sounds very laboured, particularly when I first boot up. I have read somewhere that an over hot machine this can slow things. Looking at the fan it does appear to be somewhat dusty around the air inlet. I have cleared the build-up on the outside but want to know how to clean more thoroughly. Obviously I don't want to go in with a vacuum cleaner on full blast and suck the innards out of the machine! What is the best procedure for this, assuming that this may be a possible source of the problem?