To clean your motherboard first unplugs
your system power from the electrical outlet.
Using the screwdriver remove the side
covers of your computer case and put them to one side.
Check all data and power cables
connections. Inspect all motherboard PCI and AGP slots.
Remove all add-on card of your motherboard
for example RAM, modem, VGA, sound card and LAN card.
Now blow the air around all the
motherboard sides and keeping away your blower nozzle 4 to 5
inches away from main board components. You can use vacuum
cleaner also for this purpose but compressed air is the better
solution to clean a system.
At the end assemble back all cards, cables
and side covers of your system.
I recommend you doing this after every
three months if you want to save your system life.