Is it the standby light flashing? If so, I suspect your box has developed an internal hardware fault and will need to be replaced.
You can buy a used replacement box cheaply from ebay etc (don't pay more than £30 or so). Look only for DRX890 or DRX895 models as they're the most recent, albeit still from 2015/2016.
Alternatively now night be the time to switch to Sky Q which is one of the current platforms.
