People who bought their computer more than two years ago could find that it is unable to cope with broadband.

vnunet.com has learned that older PCs equipped with motherboards with low-power chipsets are incompatible with some broadband USB modems.

This can throw up a whole host of problems. Either the broadband connection cannot be made, runs at very slow speeds or is intermittent and disconnects every few minutes.

In particular there is a known conflict with some Alcatel modems, which are very popular with UK internet service providers (ISPs), and VIA chipsets used in a number of older motherboards.

These motherboards may not supply the modem with the full power required to work. The modem then begins to draw power from the PC, causing the motherboard to trigger a self-protection feature, which shuts down the USB ports.

Mike Galvin, BTopenworld's head of operations, said : "Certain motherboards have not been able to deliver the maximum current power requirement, and this can result in a variety of problems with the modem and connection."

The problem is not the fault of chipset developers, motherboard or modem manufacturers. "When these chipsets were developed, computability with broadband was not an issue," said a spokesman for Via.

Luckily, most major ISPs are aware of the problem. "There were extensive problems about a year ago but, as motherboard and device suppliers have become more aware of the problem, we have seen a continual reduction in the number of reports," said Galvin.

But these devices will only be fitted in newer PCs. The problem could re-emerge as broadband becomes more accessible, and people who have older PCs are unlikely to be aware of the situation.

"It's one of those things that you'd only spot if you pay a lot of attention to PC technical news," explained Mark Jackson, editor of online magazine, ISP Review.

If you think the problem could affect you, it is best to run your PC through some tests and ISPs can advise you on these.

If you do turn out to have a problem, there is a wealth of information on solving these issues from the web and ISPs.

Tiscali told us that, since we had alerted it to the problem, it now plans to incorporate advice into its website FAQ section.

However, Galvin pointed out that the innumerable fixes could confuse people. "I would say please, please, please, unless you are happy about downloading patches and tweaking your BIOS, ask your ISP for help first."

What you can do

"The big problem has been that there is not one solution that works for everyone. It's a case of trying a variety of things," said Andrew Ferguson, a technical writer on ADSL Guide. He recommends anyone seeking generic answers to visit the website's Q&A section at www.adslguide.org.uk.

Typical solutions include downloading new 4 in 1 Via drivers (www.usbman.com is a good resource), using a powered USB hub (some people have better results without one though) or buying a PCI-USB adapter card and adding more USB ports to the computer.