Did you try installing a new Hard drive - box failures can be down to the drive.
Mine lay down about 6 weeks ago, not so much a power on problem, but was receiving no signal on line 1 input. Rang through, they quoted ?60 to have a call out to repair or swap the box. I said I couldnt afford it and to put me through to the cancellations. Once on cancellations they offered me a free call out if i stayed on - i agreed - they were out in 3 days and swapped it for a brand new pace.
Even if they let you cancel without the option for the free call out, you can resubscribe in the other halfs name and get a HD box now for ?49 - still cheaper than the ?60 call out and you get HD (I dont think you have to take the ?10 extra HD subscription, even though you have the HD box)