Failure to Communicate, GPS

I've encountered a problem with my GPS units and mapping software since Saturday night when I was working with Quo/Garmin Geko. It seems my PC no longer recognises any of my GPS units and none of them work with any of the mapping programs I have installed in spite of the fact all were working perfectly.

I have 3 GPS Units, a Garmin Streetpilot 3 which was working with Map Source, a Garmin eTrex Summit which worked with Memory map and Quo and a Garmin Geko which was also working with Memory Map and Quo. All the units are designed to connect using a Serial Port but were working fine using an RS232 adapter which allows the data cable to be attached to a USB socket, I have to connect via USB as my PC doesn't have a Serial Port. Now nothing works, when I connect the units I get a variety of messages but all say pretty much the same thing, Windows doesn't recognise the hardware!!

I've tried un-installing the drivers, re-installing the drivers, system restore, disconnecting/re-connecting the units but to no avail, there's simply no communication.

I know that when using Memory Map the GPS unit communicated via Garmin Serial Protocol COM7 (port) and while I have a choice of 9 ports none of them can establish a communication. Using Quo and selecting Garmin Serial Protocol no ports are displayed and attempting to connect the Streetpilot 3 to Map Source results in similar messages.

I've tried everything I can think of apart from a full PC reformat which isn't an option. I've posted a variety of screen shots in the hope that somebody, somewhere knows what the problem is. If I can't sort it I'm left with 3 GPS unitsand 3 mapping software programs that are effectively useless. I don't have Windows Auto Update enabled so again I can't see how anything could have changed, I'm inclined to blame Quo as it's really the only thing that's changed but to be honest I don't see how it could have changed anything. Maybe I should un-install Quo to see what happens?