I have a stoves 720ef anf for no obvious reason the clock resets to 23.59 and the oven turns off, can you suggest anything

The handbook says:-
To cancel the automatic setting and return the oven to manual operation, press the cook time and ready time buttons simultaneously. These are the second and third buttons from the left. If you have done that and it is not working, try turning the complete oven off for awhile - say 30 mins and turning back on. If this still doesn't work then it may be that the timer/clock has gone faulty.

Try turning the power off to the oven totally and leaving it for a few mins, then turn it back on. If this doesn't work you may have to have a new clock/timer. espares used to have them. If you don't see it listed, send in a request.

Sorry, I only deal with STOVES 720ef. Suggest you post this on a more relevent section.

It looks like the clock is on its way out. I would try two things. First, turn the power off at the main switch, leave it off for a few mins and then turn it back on and see if it makes a difference. You may need to do this a couple of times. Secondly, with the power switched off, repeatedly press all the clock buttons one at a time a number of times - there may be a contact that needs cleaning by operation and then see what happens. if you do need a new clock/timer then ask espares for a quote.

The clock is on auto because of power cut, you need to reset it to manual to enable the oven to work as normal. Refer to your user instructions.

What happens when you turn the power off to the whole oven, leave it off for a few mins and then reapply? If the automatic is still set it could be the clock is faulty.
Have you tried resetting the clock as per the handbook?

When you turn the oven on, does the background cooling fan come on at all?
Also, is the time set on the clock, and everything else set to manual running.
(With some manufacturers the oven will not work if the power has been removed for any reason. Until the time is set on the clock, power is witheld from the oven).

does anyone know were i can get a replacement top oven inner glass for my stoves heritage 720EF ?

It appears to be a wiring fault.
Suggest a job for an electrician

I have a Stoves Newhome EL716 double electric oven and last night, it just lost all power and stopped working - no grill, oven, lights, clock or anything. Can anyone tell me what this could be please? Thank you.