Probably the sensor is damaged and time to replace the scales unless it is still under the manufacturers warranty, in which case, return it for service.
O-ld is 'overload'. There are some fixes here. The first thing I would do is remove the battery and leave it overnight. Replace the batteries with new ones. If you think it may be possible that you are overloading the scale, put a bag of sugar or flour on them to test.https://www.google.com/search?q=Salter+bathroom+scales+0-ld+code..
Either you are trying to weigh something that is too heavy or the damage has already been done and the sensor has been damaged with excess weight. I bought a set just recently from ASDA (Wallmart) and they cost less than £10.
