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I haven't tested the possible solutions above yet but all are very helpful, thanks!
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I haven't tested the possible solutions above yet but all are very helpful, thanks!

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I've got a 3 year old Dell Optiplex 755 desktop PC which the fan is running excessively fast/high/noisey even though I've thoroughly sprayed out the dust from inside the PC case. What would cause this? Thanks.
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I've got a 3 year old Dell Optiplex 755 desktop PC which the fan is running excessively fast/high/noisey even though I've thoroughly sprayed out the dust from inside the PC case. What would cause this? Thanks.

PC fan running excessively

A personal computer is a general-purpose computer whose size, capabilities and price make it useful for individuals, and is intended to be operated directly by an end-user with no intervening computer time-sharing models that allowed systems to be used by many people, usually at the same time. Personal computers may be connected to a local area network (LAN), either by a cable or a wireless connection, and through that to the Internet. A personal computer may be a laptop computer or a desktop computer running an operating system such as Windows, Linux or Macintosh OS.

Hardware includes cell phones and other digital living devices, tablets, computers, servers, peripherals and components, printers and scanners, gaming consoles, networking hardware such as routers, hubs, switches and modems, storage devices and security equipment such as firewalls and other appliances.