I use a nullmodem cable to transfer data from an old PC controlling a scientific experiment (custom software for DOS). I have been using this method for the last 15 years on probably 8+ different PCs (always connecting to the same old PC). I have been using this method since Windows 7 came out also on my current PC without any problems. Recently, I had to reinstall Windows 7 and since then, the connection is asymmetric: using terminal emulators, I can see any key typed on the old computer in my win7 terminal, but nothing I type in my win7 terminal appears on the old computer. The hardware is identical and untouched, only win7 has been reinstalled. To make sure no hardware was affected accidentally during the install, I have used two different USB-to-serial converters, a PCI serial card and two different nullmodem cables - all with no effect whatsoever. Bidirectional connectivity is required for Z-modem download of the data to the new PC. Does anyone here have the slightest idea why the serial port is now so asymmetric, after the reinstall, but worked just fine on the same machine with the same hard- and software before the reinstall? I've been solving my computer problems myself for as long as I can think, but this problem stumps me and my colleagues here at our university.