Regular hardware maintenance is required for a PC about
every six-months. This involves unplugging the PC, removing
the cover and using compressed air, cleaning the dust and
lint from the fans and the components on the motherboard.
Dust/Dirt prevents proper ventilation.
A PC's biggest enemy is "Heat". Dust traps heat, Heat causes
electronic components to age faster. Check the fans for
free movement. Most commercial PC's do not have enough
fans. Most rely on the exhaust of the Power Supply. They
don't install an intake fan as it increases the noise level of the
computer. In your case, it could be heat related, or that the
Power Supply can't supply adequate Wattage. (300+ is now
considered a baseline). If you've recently added hardware it
could be raising the power requirements beyond your power
supplies capabilities. If you are uncertain about "Opening" the
case or uncomfortable with cleaning the machine locate a
local PC shop that will do it for you. While there ask them to
install a front-panel intake fan (<$10).
The amount of dust/lint inside the computer also depends on
where it sits (Floor - dirtiest), sitting on a desk it will not
collect as much.
