External HDD Affecting Internet Connection On Unconnected PC?

[squidgelet10]

Hi guys.
I am trying to find the cause of this odd phenomenon please. My own computer tech cannot come up with a logical answer.
My colleague has his PC in an adjacent room approximately 20' (6 metres) away.
We both share the same landline for internet access using two separate USB modems, one being unplugged from the telephone socket whilst the other is in use, so there is no wired connection between the two PC's apart from the mains supply. Neither PC has wireless capability.
When my colleague is connected to the internet, he loses his connection whenever I run my external USB HDD.
This does not occur the other way around, although I lose my own connection if I run the External HDD.
Anyone out there know of a possible cause/cure please?
Cheers.

[ChuckFickens]

First thoughts.... Impossible!

Guessing all that could possibly cause it would be something like badly shielded data or power wire to the hard drive being run right alongside the telephone cable.

[rojash]

As chuck says - if the conditions are exactly as you describe - impossible.
Usually in mysteries like this, it turns out that you've all overlooked some other factor.

The following is intended as an example of the sort of things that get overlooked, and not a suggested diagnosis:

When you use your external hard drive, you unplug something else and connect the power supply. The thing that you unplug just happens to be the extension lead into which your colleague's modem is plugged.

[squidgelet10]

Nice try, but NO!
Both rooms have separate ring-main sockets.
Both rooms have separate 'phone sockets.
Nothing is unplugged to plug in external HDD, which is permanently USB'd into my PC. I just plug the power supply into a trailing 4-x-socket-box which is also plugged into my own ring main socket.
Both PC's and connections are totally independent of each other and are totally self-supporting.
I'm glad someone else is baffled too!
Cheers.

[rojash]

"Nice try, but NO! "

You clearly didn't read the bit where I said "The following is intended as an example of the sort of things that get overlooked, and not a suggested diagnosis"