The most likely cause of a computer slowing down is spyware.. try these
measures first.. also check that your hard drive is not near capacity..
Some basic steps to removing Spyware/Adware..
First step is to run a one shot virus remover.. I have found that Trend
Housecall works for people.. download and run it..
http://housecall.trendmicro.com/
... select the 'online scan' and follow the directions given.
This takes a while to complete but is a necessary first step.
You will also need to download Spyware removal software.. Spybot and Adaware
are available at these websites.. both are free.. download and run them..
don't forget to check for updates after you have started them..
Adaware SE -
http://www.lavasoftusa.com/software/adaware/
... and how to use it..
http://www.bleepingcomputer.com/tutorials/tutorial48.html
SpyBot S&D -
http://www.safer-networking.org/
... and how to use it..
http://www.bleepingcomputer.com/tutorials/tutorial43.html
Spybot has the ability to immunize a system, but there is better for this
function, so download and run Spyware Blaster too.. again, check for
updates..
SpywareBlaster -
http://www.javacoolsoftware.com/spywareblaster.html
... and how to use it..
http://www.bleepingcomputer.com/tutorials/tutorial49.html
NOTE.. FOR Windows 2000/XP users ONLY.. Ewido online scan -
http://www.ewido.net/en/ ..
The full installable program has been replaced by AVG Anti-Spyware 7.5 since
the takeover by Grisoft
CWShredder will eliminate CoolWebSearch and variants.. there is a free
download here..
CWShredder..
http://www.intermute.com/spysubtract/cwshredder_download.html
To use CWShredder, simply start the program, use 'check for update' to make
sure you have the latest version, then hit 'fix.' It will check your system
against a list of current CWS variants, and fix any infections it finds.
You must also run a firewall and anti-virus program.. here are some links
for you..
Zonealarm Firewall (free)..
http://www.zonealarm.com .. recommended
AVG Anti-virus (free)..
http://free.grisoft.com/freeweb.php/doc/2/ ..
recommended
The weekly 'housekeeping' will not take long.. run Adaware, Spybot, and
SpywareBlaster weekly, ensuring that you update them prior to starting a
scan.