I leave my DTR4000 box from BT in stand by mode when I am not using it, today have noticed that there is no red light on the front of the box, the box is plugged in and switch on, so I switch the box off at the back then back on and then the red light came on, switch the box on using the remote and the light changed to blue and the BT wakeup appeared on the screen, then the youview logo appeared, then this went off the screen and the blue light went off and left it for about 1 min but nothing else happens.
This is not the frist time this problem has happened, this problem happens about every 6 months ring BT and they send me a replacement box.
have you tried setting a diferent standby mode ? Do you have mobile devices registered since this automatically stops it going into deep sleep. It sounds simmilar to problems I had until I stopped it going to deep sleep, eco mode what ever it's called.
Also have you got the latest software on the new box ? Might be worth forcing it to check from the setup menu. Also did you swap over the PSU brick as well as the box ?
Two years and going strong with mine. although it always has got suprisingly warm, the hardware seems pretty reliable.