I'm not very good at server administration, I stick to WHM, but my server is now experiencing a DDOS that hasn't seized up at all. My server is brought to it's knees. Can anyone give any advice?

What is your web hosting provider? I believe the first thing you need to do in this situation - call them

I agree with SP. Call them and explain the situation, and they will get technicians on to stop the attacks.

If you do not have any tools you need to switch your server off and wait a bit. That is not a picnic to fight against them

The DC may nullroute your IP if you don't act quickly.

Am not an expert But Turning It off blocking the Ip From which the DDos is Done Would be good and calling Your Host