A PC generates a lot of heat and heat is a major enemy of electronics. So it is important to keep your PC running cool. Most PCs employ a combination of heat sinks and fans. All power supplies incorporate a fan. Most CPUs have a heat sink and a fan. Many PCs have another fan inside the case to circulate air and some have fans just for cooling the drives.
Because these fans have moving parts and they always run while the computer is on, they will wear out. It is not uncommon for a fan to wear out in just one year, although many run for years.
If a fan in your PC stops running, it is critical that it be replaced. Your PC will run without an operating fan, but possibly not for long. It is never wise to run the PC if there is a possibility of overheating. A system that overheats may malfunction, shut itself down or some of the components may be destroyed Fortunately, fans are inexpensive and relatively easy to replace.
While the fan in the power supply might not be replaceable, the cpu, case and drive fans are replaceable.