ok heres a few tips for you
1. clear up your start up
when the computer is starting up you only need the operating system, drivers and security/anti virus software to load anything else like msn messenger etc... can be turned off for you to bring up as/when you need it
go into msconfig, go to run on start menu and type in msconfig, then go to services tab select hide microsoft services and then deselect anything like messenger (anything that you are not too sure about leave alone), then go to boot tab and do the same
doing this will speed up the loading of windows as less resources are taken away at the start up
2. check for and remove spyware
most anti virus programs can do this so run a scan using your anti virus program, if you don't have one or nothing is found then consider one or all of the following
advanced system care free version (link)- http://download.cnet.com/Advanced-SystemCare-Free/3000-2086_4-10407614.html?part=dl-6271865&subj=dl&tag=button (link is provided by download.com which is a trusted mirror for this software)
using this software it can scan for and remove malware also it offers improvements in the registry etc..
glary utilities - http://www.glaryutilities.com/gu.html
another registry cleaner that also has a malware scanner
also consider using avast anti virus home edition and threatfire both are free but powerful anti virus programs
http://www.avast.com (look for free version)
http://www.threatfire.com
both programs can scan for and remove malware and rootkits
hope this helps you
please feel free to email me on my profile if you need more help or advice, i will help you as best i can