Extremely slow Internet

[yokobr]

Hi guys. I have a dedicated link, and it got too slow since 2 days ago.
It was working pretty well, but i dunno why it got so slow.
My server runs webservice (some few webpages), shares internet connection through squid, mail service (not yet running, but it will). It's located at 192.168.0.1. Also i have two other servers: one for mysql at 192.168.0.4 and other for Active Directory at 192.168.0.16, user shares and printer service.
Now i've made a simple server to substitute my zentyal server, with windows xp and a simple proxy and it's working well... so the problem is not on my ISP.

Edit: Oh, and i forgot to say that DHCP server doesn't start by itself. I have to make a new dhcpd.conf and start it manually.