Windows 8/8.1 are NOT supported in PL-2303HXA and PL-2303X EOL chip versions.
Run PL2303 CheckChipVersion tool program in Windows XP/Vista/7 to check chip version.
Windows XP, 2000, 98 and Windows ME driver technical support is discontinued.
Prolific recommends to use PL-2303HXD (HX Rev D) or PL2303TA chip.