My broadband connection keeps cutting out, its to do with my usb port. what can i do to fix the problem?

I have bought and fitted a new usb pci card (2.0) but it still cuts out. the broadband company i use said it was that the old ports could not handle the new 8 meg broadband. its not the modem or the connection as it works fine on my laptop and the computer that has the problem was fine with 512k broadband from the same provider.
Answer
An ethernet (cat5) cable is much faster to use, and it will fix your problem because it has its own ethernet jack. (for broadband using ethernet jac you can get speeds over 120 mbsec. with usb not more likely to get more then 100 mbsec although this may not seem like much its a huge difference espically when downloading large files or running complex files via internet. an ethernet cable looks like a large phone wire and is normally yellow or blue but you may find it in an assortment of colors.