I have a Mac OS X v10.5.8 and my Safari version is 5.0.6 (5533.22.3).
Your operating system version and Safari are severly outdated and possibly compromised by the Flashback botnet.
It might be your new ISP see's it and is blocking your machine in order to get you to fix your problem.
I suggest you get offline, then backup your users files manually to a external drive (emergency quick copy method)
then take your machine (and all your disks and software) to a local PC/Mac specialist and have them upgrade your machine with a fresh install of 10.5 + programs (including iLife) then upgrade to 10.6.8. Snow Leopard.
They wil have to order a disk overnight, but after that it should be done.
Also max the RAM, upgrade the hard drive to 7,200 (no hybrids or SSDs) and have them check behind your fans for dustbunnies. Clean the machine.
Do not go to 10.7 or 10.8 on that machine, it's too old and at it's end of life stage, also you don't want to spend more money having to replace nearly all your software that 10.7-10.8 requires.
That machine is five years old, it's about to die, unless you haven't been using it much. but you can likely can get another 2 more years out of it with the steps I mentioned.
Later you can use the new internal drive for backup on a new machine if and when it does die. (it might not!)
If you take the machine to Apple, then they are going to hobble it with 10.7 or 10.8 and not install 10.6, also charge you a fortune for a new drive and RAM, that your just going to get a new machine instead.
When you get 10.6 installed, install Firefox web browser as it gets updates and much faster, Apple did not release Safari 6 for 10.6