My cactus is dieing and i don't know why, it might be because i give it too much water. The cactus is all squishy and bits are falling off, though i can't really do anything as i'm at university and have no tools here :(
Hi Laura, you've pretty much answered your own question. The overwatering thing is the primo reason for killing off these tough plants. They are only able to withstand drought; they can't withstand drowning.
For this one, I'm sorry but there is no hope. Once pieces start to fall off, it's a sign that the interior of the plant is completely rotted away.
In the trash, and buy a new one - but don't over water it! You can see more about these intriguing plants here: Cactus plants.