URGENT computer help

Ok, well guys. I am in need of urgent help from you.
I have a Dell Dimension desktop computer running Windowns XP with Internet explorer 6 with Tiscali as my ISP.
In the last two weeks I have been recieving a message when I 1st turn on the computer saying
"Other applications currently occupy USB bandwidth. Please close all other applications then remove other USB devices. Click OK to continue"
If I press cancel then it continues to appear every two minutes but if I press the only other option, OK, then I get a new box coming up saying,
"Please wait while modem is adjusting the USB bandwidth"

Even after that when the box goes the same first message comes up 5 minutes later.

This USB bandwidth problem happened at the same time as problem two. I am not able to connect to the internet, whenever I try to connect it just says no dial tone. Now while this sounds like a problem with my internet connection equipment I am strangly able to connect to the interent when someone is using the phone or the phones off the hook.

I need the internet so at first I called tiscali. They are crap. I called them a total of 5 times and was on the phone to them a total of around 3 hours. They did nothing, they sais swap my filters around and that didnt work, they said buy new filters and that didnt work. They were awful. Then today I called out BT as I thought it could be a BT line fault. They sent a man out who spend 4 hours at my house, he tried everything but couldnt do anything about it, he believes its tiscalis fault.


So at this point Im on the net with the phone off the hook and that can't go on, so basically if any of you have any ideas I will be ever so grateful. What can I do?
Thank you
Joe