Same problem here. I'm about to throw the thing against a wall.
I don't think it's a problem with the PC though. The key shorts (TX) even when the RS232 isn't connected. It's not a mic problem being as I only wanted the thing to use as a keyer.
I have tried all combinations of Key jumpers, including none at all. I've looked at the schematic and the only thing I can conclude is that the IC "U2" is fried.
Please for the love of God, help me!
Compaq Armada e500 1GHz PIII 384MB SDRAM WinXP ProSP2.