Exclamation mark in Device Manager, and the following error?
This device cannot start. (Code 10)
A device which does not exist was specified.
Cause: PL2303 chips are fake! In the newest drivers Prolific blocked all fake chips and the driver in Windows 8.1 is also blocking it.
But there is a solution – you have to install old drivers – version 126.96.36.199
Driver and more info available here: Fake PL2303 - how to install on Windows 8.1 - BartB