I have a 1999 Toyota Corolla and electronic key

I have a 1999 Toyota Corolla and electronic key system has only locking button. The unlocking button is lost and I was told I need to buy one online. Last night after coming home I have locked with electronic locking button and doors got locked. Today I have opened the door manually with the key and tried to start the car. It automatically triggered the theft alarm and red light besides steering is blinking continuously. It disable the car starting. The alarm comes only when we try to ignite the car. But the light keeps on blinking. When we disconnect the battery the blinking goes off, but when we reconnect the battery the blinking comes on. We do not know the reason for this and we don't know how to start the car. I appreciate any advice given in this regard.
Bose.