Can you please advise the model number of danfross timer?
In most cases a simple power cycle should recover it back to a working state, the power is derived from the boiler so powering off the boiler should shut down the programmer.
The second thing to check is that none of the buttons on the timer have become depressed\stuck down.
As per out conversation after a power cycle the unit is still locked up this would suggest the programmer is faulty and needs to be replaced, you can buy a replacement from screwfix for around £55. Please make sure you switch the power off to the boiler before attempting to remove the programmer.