X provides the GUI. KSysGuard is a KDE system monitoring tool; I don't use KDE, but perhaps it can be removed from the list of startup applications. Based on this article
, it doesn't appear to be an essential KDE process.
Neither should put a significant load on your system, unless your system is seriously underpowered; you can run top
in a terminal to see what processes are eating what resources.
Based on your statement about the fans, my first guess is that your system may not be cooling properly. Make sure the vents are clear of dust and that the fans are blowing air. If it's a desktop, open the case and make sure the CPU and CPU fans are clear of dust. Dust is an enemy of computers; it also conducts electricity and, in extreme cases, can short circuits. A can of compressed air is recommended, as an electric vacuum cleaner might cause static.
You might also use a monitoring tool, such as KSysGuard, GKrellM, or Conky, to monitor the CPU temperature.