I think i have worked out its when i have downloaded and uploaded a certain amount (normally when its between 1gb and 2)
I have no idea how to fix it, none at all.
Had this problem for about half a year now, all i do is turn it off by the power button (which is bad i know)
Tried reinstalling, clean formatting everything.
Happens to my friend as well (we have the same adsl modem, a USB bt voyager one), i thought we were the only two it happened to till i saw this thread!