Tiberian sun lockup with cable modem

[denissimo]

whenever I play Tiberain sun online, the game and the computer locks up when the game is either won or lost.
This only started happening after I went from a dial up modem to a cable modem.
I have tried everything from software updates to a complete reformat and reinstallation of just the basics to see if there was a conflict with other software.
I have been in touch with Westwood who make the game but all I get is automated responses with the common faults and cures listed. (basically, they haven't a clue what's wrong)
Before this started happening, me and my son were in the top 10 in the world rankings and now we are getting serious withdrawal symptoms.
Any help or advice would be greatly appreciated.

[glc]

Is your cable modem internal or external - and if external, is it connected by Ethernet or USB? Whatever it is, is it sharing IRQ with any other devices?

[denissimo]

Its an external running through an Ethernet card. I have checked, and it is not sharing an IRQ with anything else. If I revert back to a dial up modem, the game plays perfectly normal.