If you gotten a used computer, it should have come with the operating system
software on CD.   I strongly recommend reinstalling the OS (and reformatting
the drive) to make sure you are not using a virus infected system.
Suggested steps for reinstallation:
- Boot with your Windows XP CD in the CD ROM drive
- If you have a broadband connection, make sure that it is plugged in (to
get all the critical security fixes automatically from Automatic Update)
- When prompted, DO NOT reinstall Windows
- Select your partition, choose format
- Create a strong administrator password (use a combo of upper & lowercase
characters and symbols).  Be sure to write it down someplace you will
remember to look for it if there is an emergency.
- Visit 
http://www.microsoft.com/security/protect/ to walk through enabling
your internet firewall and get security patches from Microsoft
- Install antivirus software
- Install all your apps
- Configure your email
- Create a System Restore Point
To create a Restore Point
1.. Access the System Restore Wizard through Help and Support Center.
2.. Click Create a restore point, and then click Next.
3.. In the Restore point description box, type a name to identify this
restore point. System Restore automatically adds to this name the date and
time that this Restore Point is created.
a.. To finish creating this restore point, click Create.
b.. To cancel restore point creation and return to the Welcome to System
Restore screen, click Back.
c.. To cancel restore point creation and exit the System Restore Wizard,
click Cancel.
Remember to regularly backup your files to CD or disk and you will be set!