If you have purchased a new computer, perhaps have built your own PC or have a PC/notebook which is over a year old, you should check these things now and at least once a year.
Introduction
Modern computers are able to monitor various temperatures, fan speeds and voltages throughout the system. You can easily download software to display these values (often the BIOS setup/configuration menu system will display them too). Using SMART, we can also find out about the health of our internal disk drives too.
If you have received a new or second-hand system recently, a typical problem is that during transportation, the CPU heatsink may have come loose. This would mean that your CPU will get too hot and when this happens, modern PCs will usually 'throttle back' and go slow to avoid permanent damage to the CPU.
If you have a computer that is a few years old, the thermal paste between the CPU and the CPU heatsink may have dried out. Again, your CPU may be getting too hot.
Also, if your PC\Notebook is older than a year or so, it may have accumulated dust and cobwebs! This can seriously affect the air flow through the system and can thus cause the hard drives and CPU to overheat.
If you have overclocked your system, you will need to be particularly careful, because you are probably running it at its maximum performance capabilities - any overheating may cause damage or a system crash!
Some monitoring programs which I recommend you to try are: