Why is my computer running extremely slow?

This is a basically new laptop computer

its a compaq presario v5000

just reinstalled windows about a week ago ,then it was running really fast
but after a week its really slow

so far ive only installed an anti virus cd

please help

also didnt want to spend money

Is the computer Running slow while surfing the internet, or when running programs? Using a registry cleaner can clean up your computer and then make your computer faster,Why?the reason is that there may be some registry errors and remnant,corrupt files and temp files in your computer to cause "computer slow". Every time you install and uninstall software on your computer and surfing online you create junk in the computer registry.over time, the registry can grow to enormous proportions, especially if the various programs you've installed do not do a good job of deleting and/or updating it's Registry entries.You need to scan and clean your computer with registry cleaner to make it fast. if your problem is with programs running slowly- I can advise you to download this software, which can extremely help- CCleaner .Good Registry Cleaner will improve your computer and Internet performance dramatically! Do all these and Perform speed here scanmyspeed.com once it will sounds better ...