I just brought one of these computer used for $20, it had the same problem the CPU fan would roar after just a minute of two once booted. No doubt this is why someone donated to the charity store where I brought it.
The problem with it was the CPU heat sink was clogged with dust once I clean this out and the rest of the cabinet with compress air it reduced the fan noise by about 90%. Be careful taking the heat sink off the CPU it is delicate.