Car battery

A few days ago I left the lights on my car and forgot to turn them off, a few hours later the car was making a alarm sound, so I went to my car and tried to turn the car on but it would not start and only the ignition came on.
A few days later my friend brought his car over and we used a damaged jump lead to try and jump start the car but this did not help.
when I put in the key to try and start the car nothing came on, not even the ignition.
what can I do?
should I try to jump start it with a new jump lead?