Is it time to defrag your PC? Overtime, files get fragmented due to copying & moving files around, deleting files or installing applications on the hard drive. For example, let's say you had lots of music on the hard drive but decided to delete it. Now, all of the space where the music was is empty and ready for more files to be stored. Problem is that depending on how big the next program or file you attempt to install is, it may just not "fit" into the empty space vacated by the previous music files. Windows may have to find the next available space to finish the install of the program or file. This is what causes the fragmentation of the hard drive, which can cause the PC to respond slower because it has to work harder to find all of the files related to the program or application you are trying to access.
Solution: Defrag PC on a regular basis if you do alot of moving, copying or deleting of files or programs. On Windows XP, you can schedule a defrag or start one manually. Windows Vista attempts to automatically defrag when the PC is idle (but it is also scheduled to defrag as well by default).