ADSL restarts computer

[rtv]

When I access the internet via broadband (ADSL external Modem) I often get powered down and automatically re-started.  My service provider said it was a power problem and to install a pc USB card.  I did and nothing changed.  I consulted everthingusb.com and was advised to upgrade fom my 359 watt power supply to 450 watt.  Done that - no change.  It doesn't happen all the time. It happens most often when trying to start my internet session but then usually works ok when I try again.  Only occasionally do I get a restart during a session.  I am using Windows 98 on a Time pc.
Help would be much appreciated.  

[Raptor]

Scan for viruses, spyware and trojans

[merlin_2]

untick the disable usb corrections box. how many usb devices have you got?. check the power options in the adapter tab to never

[rtv]

Thanks Raptor - I've done th scanning bit - nothing found.

Thanks Merlin 2 - Can you tell me where to find the disable usb connections box to tick and the adapter tab?

[merlin_2]

right-click the my computer icon....properties click...device manager click...scroll down thew list to usb icon click the + sign click the usb  host controllers...then click the properties tab ..then click the advanced tab...and untick the disable error dection box ..done...what modem are you using speedtouch/sagem?

[rtv]

The 'disable error detection' boxes were already unticked.  There are several usb controllers listed - all unticked.  My modem is a BT Voyager 100.  Any more suggestions will be welcomed.

[merlin_2]

click on device manager', expand the 'network adapters' section, double click on the Voyager100  icon, select the power tab and uncheck the tick that says something along the lines of 'allow this device to be turned off to save power and reboot your comp if not ask bt for this one>Voyager 200