Do you have a VPS or Dedicated server? What are it's specs (Processor, memory)? How many active (And reasonably trafficked) proxies do you have running on it?
Here is mine
VPS with 768 MB Guaranteed (1.5 GB Burst RAM) and 1TB bandwidth/month.
It has only one active proxy with 2000 UV's/day on it, but that is enough to crash the VPS every other day.