Option A — Using an installer (recommended when available)
Right-click the faulty device in Device Manager, select Uninstall , unplug the adapter, install STEP 7 V5.5 SP3 or the standalone driver package, restart, and plug the adapter back in. "Driver Not Digitally Signed" Warning Cause: Windows XP SP3 strictly checks driver signatures. siemens pc adapter usb a2 driver windows xp