A Very Common Problem...
So many people tell me that their PCs have become "sluggish" and unresponsive. It could be that doing anything takes much longer than it used to take or the PC takes a long time to start up. It is often a case of having to wait for the hourglass to finish even when nothing is being done on the PC. If you have this problem then be assured that it is not a case of the PC "doing nothing". If the hourglass is going for long periods of time and the PC seems to be busy even when you're not doing anything on it then it is a sure sign that something is going on in the background. The PC is doing something. It just may not be doing what it you want it to be doing.

Spyware and Malware...
Many people have spyware and/or malware on their PCs even when they believe themselves to be protected. There is no panacea of anti-virus programs and unless a combination of good tools is used in conjunction with each other, some malware is bound to slip through the net eventually. Both spyware and malware will slow down the system. (CLICK HERE more about "Spyware, Malware, Viruses and RATS").

Windows is not built to last forever...
Windows gets clogged up with old software and applications can leave bloated "tools" installed and more often large amounts of data in the Registry. Your system background can become weighed down with tasks that load silently at start-up and essential system programs can be forced to perform non-essential cycles induced by other installed/uninstalled software. It's hard to rectify all these problems through tweaking alone, and due to the way Windows was designed the best option is to simply start again. Viruses and spyware can also damage a system to such an extent that repairing Windows is not a realistic option and re-building from scratch is the only way to proceed.
(CLICK HERE to read more about "Reinstalling Windows and Applications").

Bad Housekeeping...
"Housekeeping" tasks that all Windows users should be performing on a regular basis include un-installing applications that are no longer being used, defragmenting hard drives and using the Windows Check Disk utility.
Unfortunately I've known people who have been using a PC and have never used the defragmentation utility in all the time they've owned it; in one case this was three years. Under these circumstances it is no wonder that the machine is grinding to a halt.

Background tasks that are no longer needed...
Software designed to drive periferals often gets "left behind" long after the hardware is gone. If you buy a new printer then background tasks designed to function with your old printer are often still there, running in the background and using up your processing power. This applies to scanner, cameras, expansion cards and pretty much and hardware that can be added to a Windows machine. The fault often lies with software not being uninstalled in the first place by the user but is also the fault of Windows itself which has been designed to hold on to drivers on the principal that it may need them again in the future. Your PC might be running slowly simply because it is still yearning for you to plug in that old 2 megapixel camera that you sold three years ago on eBay!