PC World - PC owners know that every computer has a unique assortment of components, applications and peripherals. Nevertheless, certain things--including a host of common PC problems and mysteries--are part of the shared experience of computer ownership. The editors at PCWorld have seen and solved hundreds of PC mysteries, ranging from balky printers to diffident video players to persnickety file attachments. Most of the answers to these tech questions are simple and straightforward, so we've taken the liberty of compiling some of the most frequently encountered PC mysteries into a single list that we'll update regularly. Following each question we provide a short response that summarizes what we know. For a more detailed explanation and some helpful tips, click the links in each answer.