Next time you reboot your PC, spend half a minute in the BIOS - it'll give you vital information about the health of your PC. Here's how...
Accessing the BIOS
BIOSes vary but generally it's a matter or rebooting your PC and pressing [Del] repeatedly as it starts.
If this doesn't work, check your PC's documentation to find out the key combination.
Once there, use the keyboard to navigate.
Select PC Health or System Monitor.
This screen has details on voltage to components, the temperature of the CPU and the overall system, and the fan speeds.
In this case, they're not working and so need attention.
While in the BIOS it's worth checking that hard drive SMART monitoring is enabled.
You'll usually find it under BIOS features setup.
When it's on, you can run software that can predict hard drive errors before they happen.