There can be any number of reasons the computer is running slow, However the most common reason (besides virus / spyware /adware) is from the lack of cleaning the computers temp files and not rebooting the computer every so often. (keeping the PC on 24x7)
Ill be honest, In the time it would take me to type out all the areas that need to be looked at I could fix the computer remotely… given you have a broadband internet connection.
But anyway, here is a quick list off the top of my head to look into. Rather than typing out how and where everything is, ill let you know what to do and if you need help feel free to email me.
C:/ settings: (I suggest doing these last and in this order)
Run disk cleanup
Uncheck allow indexing
Run Defrag
Internet settings:
Delete cookies
Delete files (and offline content)
Set history to 0 days
Change temp internet file space to around 256
Clear history
(First make sure you can view hidden files and folders)
DEL contents of following folders: (or make sure they are empty)
(C:\Documents and Settings\YOURUSERNAME\Local Settings\)
TEMP
TEMP Internet files
History
(C:\Documents and Settings\username)
Recent folder
Check your Windows folder
You should see a lot of windows uninstall folders in blue and shaded out (compressed and hidden) You can DEL all but the latest one (looks something like $uninstall something.
DEL anything from startup you don’t need running
Either via msconfig and/or regedit in your run folders under current user and local machine
Change the space allocated for the recycle bin to 1-2% of drive space.
Set virtual memory to about 1.5X your installed memory (ex 1GB mem, set to 1536)
These are just some of the steps I take when building a new computer for someone.
SO this is just my 2 cents. You may or may not want to change some of the options (for example, you might want to have 30 days of past history saved for your internet)
I don’t know, there is so much more that can be done but this is a good start.
Hope that helps - I gotta get back to work.