UPS Problem

[necor]

hi everyone, i have two tedelex model: intellipower - 4 24VDC ups, the problem is that they cant power on (up) even when connected to a working socket. They have to 12V batteries which are also kinda flat but still i believe the ups should be able to power up even when just connected to a well powered and working socket. what can be the problem and whats the best solution you can give in order for me to fix them?