A customer once asked me "Is there any free software that allows me to see and disable unwanted programs running in the background?"

Probably, but I know something better than free software for this job: software that comes with Windows. All current versions of Windows come with a tool to help you trim back what's running at the moment.  The look, behavior, and feel of this tool changed drastically (and for the better) with Windows 8. I'll cover Windows 7 and Windows 8 here, but the Windows 7 directions should work reasonably well with XP and Vista. The tool is called Task Manager. To open it, right-click the taskbar and selecting Task Manager or Start >Task Manager, depending on your version of Windows.

Windows 7
In the Windows 7 version, the Applications tab displays currently-running applications. But what's the difference between an application and a program? In this context, an application is a program with its own window--either visible on the desktop or minimized to the taskbar. For instance, your browser, if it's running, is an application and is listed here. Your antivirus program won't show up in this list until you double-click the tiny icon in the notification area and bring up the window.

All applications can be closed from within the application--you just click the X in the upper-right corner. But if that doesn't work, you can use the End Task button on Task Manager's Applications tab. But if Windows is overloaded, the problem is probably not applications, but processes--threads of code running in the background. So click the Processes tab. As I write this, the Task Manager tells me that I'm running three applications, but 134 processes--16 just for Chrome.

Windows 7 Task Manager Processes
The Processes tab is laid out as a table, and like most Windows tables, you can sort it by clicking the column headings. Click Image Name, and you alphabetize the processes. Click CPU, and you can see which processes are hogging the processor (most aren't). Click Memory, and you'll see which ones are hogging RAM. To stop a process, click the End Process button, and confirm that that's what you really want to do.

The Windows 8 version behaves much the same way. The window is better designed and easier to read, and there are a few important differences.

First of all, there's no Applications tab. But you'll see both applications and Metro/Modern Interface apps listed at the top of the Processes tab.

This layout allows you to see programs and processes together. Windows places icons next to the processes to help you figure out what program launched them. 

Windows 8 Task Manager 
But you might notice that the Processes tab lacks a Description column--a seemingly serious deficiency if you're trying to figure out what a process does. But there's a solution. Right-click the process you're wondering about and select Go to details. This will take you to the Details tab, where the Description column now lives. It will also take you to the same process, so you don't have to look for it again.

A lot of problems can keep a computer from booting Windows (or any other operating system). Fortunately, you can get a pretty good idea by noting how and when the PC fails. If you press the power button and nothing happens, you've got a very different problem than if the PC starts but Windows never loads.

Let's take a look at some of the possibilities.
If absolutely nothing happens when you press the power button, you almost certainly have a power problem. Electricity is not getting to the PC.

Unplug the power cord. Examine it for breaks or other damage. If you find damage, you know what to replace. Otherwise, plug everything back in, make sure all of the plugs are firmly in their sockets, and try again. (If the power cord is a laptop AC adaptor, check the connections between the different pieces.)

If it still doesn't work, plug something else—like a lamp—into the same socket. That will tell you if there's a problem with the surge protector or the electric outlet. If your surge protector or power strip is under your desk, check to make sure a wandering toe didn't turn it off.

If the cord appears to be fine and the socket works, try replacing the power cord or, in a laptop, the AC adapter. You may have to buy one specific to your model.

The problem could be with the power supply. If nothing else fixes the problem, consider replacing that. Desktop power supplies are usually cheap and easy to replace yourself.

That's not the case with laptops. Unless you're a very skilled technician, I recommend paying a professional to do the job.

If the PC starts, but fails before Windows can load, go into your PC's setup program, make sure that the hard drive is recognized and in the boot sequence. I went into details about this task only last month.

You might also consider booting with a live Linux disc or flash drive to see if you can access the contents of the drive.