I have been told to 'clean' my personal computer? What exactly does that mean and is it easy to do? Robert, Mid-Levels DQ: Internet browsers and other applications tend to create lots of little files, which are not necessarily dispensed with after their use. As a result, they take up a lot of space and slow a PC down. If any are malicious they could harm your computer, so you should get rid of these files regularly. A system optimisation and privacy tool called CCleaner (ccleaner.com) does the basic work for free but you can pay for more functions. Another set of tools comes from Auslogics Software (auslogics.com). The company provides a number of utilities to speed up your computer and internet connection. None of these products should be difficult to use, as they are reasonably self-explanatory. The performance of my once super-fast personal computer has considerably slowed during the past few months. It runs the Windows XP operating system and is powered by an AMD Athlon 64 X2 dual-core processor. What could be wrong? Name and address supplied DQ: All sorts of things can happen to slow a PC down over time. The two biggest villains here are 'disk fragmentation' and Microsoft. When you open and close files, the hard disk will put the data in various places and they are seldom contiguous. When you open a file (and remember, many applications today open and close files without your knowledge), the system will slow while it gets the data. There are plenty of so-called defrag software programs in the market to help you. Microsoft is to blame for burdening your computer's registry with unnecessary software. To learn how to clean up your computer, go to www.speedupyourcomputer.windowsreinstall.com . One more thing could make a difference. A friend of mine had a problem with his XP operating system not recognising his computer's dual-core processor. His solution was to download the pertinent resource from 'Athlon 64 X2 Dual Core Processor Utilities & Updates' at amd.com. As a result, he claims to have achieved a 20 per cent increase in computer speed.