MiT Ltd.

• Hardware Diagnostic
• Check Hard Drive for errors and efficiency
• Check disk space available
• Detect and fix directory errors
• Physically clean FDD & CD/DVD Drives
• Physically clean inside of computer (fire hazard by accumulated dust)
• Ensure that all software is updated
• Perform a thorough scan for intruders and discuss ways to protect yourself
• Disable unnecessary programs from starting and taking up valuable system resources
• Remove redundant software

The pictures below show the inside of a PC in a suboptimal condition...

Explanation:

In the left picture you will notice some "organic" structure in the upper centre of the pic.
That is "fluff", or a cumulation of fibre based dirt/dust.

The rectangular unit behind the fluff is the cooling block for the processor. The part that looks like a concrete wall actually should show the cooling fins of the block; the "concrete-wall-effect" was achieved by having the spaces between the fins filled up solidly with microfine dust.
Ultimately the fan stopped spinning, the PC overheated and in the end did not start at all.
Click on the picture for a bigger version with some details explained.

The right picture shows the general condition of the PC in question which -by the way- was in use for less than a year before the photos were taken...