Also check that it is the same type of RAM and is compatible with your motherboard.
E.g. ur current RAM lets say is PC3200
Ur old RAM lets say is PC2100
The old RAM wouldn't work beacuse it is the wrong type. To see what type it is, look at the RAM sticks and it will say on it.
jbennet commented: bs -4
arjunsasidharan commented: There you go!! :) +3