Bad Disk Drive Bookkeeping As mentioned in the fragmentation description above, disk drives need to keep a record of where all files and parts of files are physically located on themselves. Sometimes, that record becomes corrupted by bad data, operating system bugs, dust, cat hair, etc. This will help prevent losing files or writing over files you didn't intend to delete. Food and Drinks Food is good for people, but bad for their computers. Small bits of even the tastiest treats can become lodged between and under keyboard keys, sometimes ruining them altogether.
Drinks can cause serious problems as well.
Fluids can easily short out the keyboard, or do unspeakable things to the CPU if spilled into the case. In general, keep liquids well out of spill-range of your computer.