Updated November 24, 2014:

Computers need a good "tune-up" at least once a year. Please realize you initiate this at your own risk, we are not responsible if something goes wrong. That being said, these are the steps we recommend:

Close all your programs. Click on start, select the RUN command. Type MRT and hit enter. This launches the Microsoft Malicious Software Repair Tool. Follow the prompts and run this utility. Just do a quick scan. If it finds any suspect files, delete them.

Run Windows Update, reboot, run it again, reboot, etc., reboot until they completed. I also select the CUSTOM updates . . . www.windowsupdate.com

We are assuming you are using an antivirus program such as Symantec, Avast, McAfee, or Eset.

From the Control Panel. Remove those unused programs from add/delete programs in the Control Panel. Remove stupid things that got loaded in error, programs you never need, widgets you never used.  But do not delete something that you are not certain of.

Tip: If you are unsure what it is, open up IE and type the name of the program in the "google box".  The google knows everything. Example: What is bobstoolbox? In the event you see a program named bobstoolbox. It might be something you need, or it could be "bloatware."

Next, using Internet Explorer, download, install, and run both parts of this freeware: I would not add it to startup; I would uncheck all the little boxes, just install the basic version, and then run it. http://www.filehippo.com/download_ccleaner/8818/   

You want the option at the upper right; it's about 3.1 MB or so.

Run this utility. Skip the analysis, just click on the option to the far right, lower box. It cleans out all the unused old files. Then run the Registry utility - in that order, then reboot. It will ask you to save changes, say yes, take the defaults. This is a powerful, valuable utility. Do not let it install extra programs, Google or Yahoo toolbars, desktop shortcuts, a startup shortcut, etc. Make sure nothing extra is checked.

Next, we go after all the spyware and malicious worms:

Download and run the free version of this: 
http://www.superantispyware.com/download.html  Run it.

Lastly, download and run this:  http://download.cnet.com/topics/spybot

Doing these steps will almost always speed up your computer and make it much more reliable.