PC 's not a Packard Hell is it?
Is the PC a Packard Bell?They are notorious for various problems,also if modem is not getting enough power have you considered getting a powered USB hub, thats what I use for my Fujitsu ADSL modem, works a treat.Hope this helps.
Teddy, why are you using a USB modem?
When I first got DSL service they sent a USB modem. Bad choice, because it was a disaster. Crashed and burned. So I went to an ethernet adapter modem (Speedstream) and had no problem. Another thing is the length of the phone line you're using. I was told the limit is 15 ft. I was using a 25 ft line and got disconnected several times.
Are you overseas? This may not apply to u.