Time to buy a new computer!
[No, you cannot use the Win7 disk from your other computer.]
IMPORTANT! => The WinXP computer should NOT be connected to the internet or any other computers. All of your personal data (e.g., online banking & credit-card passwords) should be considered at-risk, if not already compromised.
• Support [and updates] for Windows XP ended on 08 April 2014
• Microsoft security research paints bleak picture for WinXP users after 08 April 2014
• Cyber threats to WinXP: Guidance for Home Users & Small Businesses