Make sure cord is plugged in, power is working;try removing the battery, carefully replacing. If there is power, your battery may be too old and must be replaced.
1) Your battery is dead. If it is older than 3 years, this is likely. 2) Your charger is broken. Try borrowing another charger. 3) The charge port is broken.
A possible reason why your IBM X21 battery is not charging can be the charging cable. You can check if it is still working by simply looking at the green led from the square like part of it. Try borrowing the same cable from friends. If it still doesn't work, then I guess the problem is the battery.
Maybe one of the factors is the battery itself. Or maybe the adapter used due to faulty circuit. Double check first the battery and then the adapter and then for you to take actions.