How can I reset my Omega Petite security alarm?

We had a power cut, which set off the alarm. The control panel wouldn't turn it off. When the power came back, we turned off and then on the circuit breaker. This stopped the alarm sounding, but the display was a red dot, none of the buttons worked. I have turned the power off and the outside siren sounded. I turned the power back on, outside went quiet, the inside panel beeped, it wanted the code. We input this, it worked, but since then, the keys won't set the system. Any ideas?