Sagem F@st 800 adsl modem not working properly

I have recently signed up with Tiscali broadband and they sent me a
Sagem F@st 800 adsl modem which worked fine for 2 months and then
started to develop problems in that when the pc booted up the power
and adsl lights did not come on and i could not connect, the only
solution to this seems to be to either pull out the the usb lead and
then put it back in until the lights come on but this can take up to
20 mins to achieve or to uninstall the usb hub and then restart the pc
which then reinstalls the usb and the modem seems to work. I called
tiscali about tis and they say that because i have a pci chip the
modem needs 500ma but the machine only puts out 400ma but i fail to
understand how this could be if as i said it worked fine for 2 months
and it works when i uninstall usb hub surely if there isnt enough
power there is never enough power, tiscali have suggested i get an
externally powered usb hub, any ideas.

My pc is an Acer T120 AMD Athlon 2400+ 266mhz
40gb hd and 256k ram using windows xp