My PC is 5 years old. I celebrated this by cleaning my keyboard.
For step wise instructions, see this site.
“Before you start, make sure you know which keycap goes where. Unless you have another keyboard to hand, or it is illustrated in the handbook, draw a diagram, take a digital photograph, or even place the keyboard on your scanner or photocopier and record the key positions in this way. Next, carefully remove the keycaps. A small screwdriver works well and is unlikely to cause any damage.
Insert the blade of the screwdriver under a keycap and lift it up. I suggest you only remove the ordinary sized keys. The space bar and the larger keys like Return and Enter often have wire mechanisms underneath that are hard to fit back into place. Having removed the keycaps, it is easier to remove the debris from the keyboard using a combination of handheld vacuum cleaner, brush and / or compressed-gas aerosol. You can also wash the keycaps, as long as you dry them fully.
Although the buildup of grime on the keycaps can be severe, stick with warm soapy water and a sponge. Do not be tempted to use an organic solvent or any cleaning agent stronger than soap and do not use a scourer. Organic solvents could dissolve the plastic of the keycaps and abrasive cleaning agents or scourers could remove the legends or scratch the keys, making them more susceptible to the accumulation of dirt in the future. Replacing the keycaps – once dry – involves nothing more complicated than pushing them down on to the appropriate switch mechanisms.”
PS: I removed all the keys, including the large ones such as the “Enter” key which had a long bent holding metal wire and two additional guides on the underside.