If the thermostat has been wiped and has no screen display then the EPROM will need reprogramming as this is a digital stat... The only real solution to this is throw it in the bin and buy a new one...
If the clock has just lost its settings, then all you need to do is re-program it... Instructions can be found here:
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix general d.i.y.