My modem has started to lose Sync & Rdy lights, not sure if it actually reboots itself, though. Once dropped off, it takes 15-20 minutes before reconnects to network
I had this problem in the past and the cause was local network issues. Engineer eventually came (having been via the 'read the script' support and told to "reinstal Windows" etc.), he swapped modem, but openly admitted there were major network issues, they knew about them, but to meet SLA they just swapped out modems knowing they wouldn't fix the problem
I notice my local my BT exchange (just down the road) is to have 8Mb ADSL next month, this may be the final push I need to leave NTL