Welcome to TSF,
Is this a Wired or Wireless connection issue?
Restore your computer to an earlier date where it was previously working using the XP System Restore.
Uninstall the network adapter from Device Manager. Reboot your computer so that your Windows will reinstall the driver. I would highly suggest for you to download and install the latest driver.
Disable the problematic Network Adapter's power saving mode from Device Manager, locate the Network Adapter=> Properties=> Power Management Tab, in here you may disable any Power Save mode options by unchecking them off.
Please post an update.