USB to Serial Data Cable

[Sudden]

I have a USB to Serial data cable which I should be able to use between my amateur radio and computer, so that I can enter frequencies etc into the radio.
I am having trouble with a no connection problem.
How can I test the cable without connecting to the radio?
From the Prolific chip/usb plug there are 3 wires to the radio one TX, one RX and ground.
Can a loopback test be performed if so how? Do I connect the TX to the RX and stand by with fire fighting equipment?

All serious help would be appreciated.
One forum I tried said buy a new cable which proves nothing.

 

[davenn]

yes connecting the TX to RX should provide a loopback use the windows terminal prog ( found in accessories) to see if text you type gets echo'ed back

Dave