Unusual OSX 10.9.2 connectivity issue

[DeathMachine]

Hello,
I"ll start off by saying that I'm not the most computer savvy person out there. Also, this is not about connecting to WiFi, I've had no issues with that. The problem I have is this:
We bought a new iMac, hooked everything up, downloaded the updates and immediately noticed we are having network issues. We've had problems with our ISP in the past and took it as a sign to change, so our all our hardware is new. The issue we're having is that when the iMac is connected to the network our internet speeds vary erratically from 10mbps to 0.25mbps. Once it is off everything runs smoothly and speeds hover around 10mbps. On the device list for our network the iMac comes up with no make or model and shows as running Windows 7. For a while other devices were getting booted off our network with an error message that their IP addresses were in use. I have also been running a macbook pro with osx 10.9.1 with no issues. Connection issues also occur when the iMac is the only device on the network.

I've tried searching for a solution but have come up empty handed. Most responses have to do with WiFi issues, which we don't have.

Thanks in advance for any help

 

[MacInWin]

For a while other devices were getting booted off our network with an error message that their IP addresses were in use.

Working from that one sentence, try this (assuming you have 10.9.2 as the OS):

Open System Preferences/Network

On the left will be a list of interfaces, one of which should be green (the WiFi, most likely). Click on that to highlight it. Then Click on Advanced button on the right and then on TCP/IP tab. Make sure that under "Configure IPv4" it says "Using DHCP." I don't know if that will solve the problem, but most of the symptoms you are showing come from having one or more devices with fixed IP numbers in an otherwise Dynamic IP network.

EDIT: If your iMac is using DHCP, then you should check all the other devices in your network to see if any of them are using fixed IP numbers. If there are such, and if you need to keep them fixed for any reason, you can either go into your router setup and define the acceptable range for the router to protect those numbers or stab around to find a fixed IP for the iMac that is NOT the same as the others. Most home networks use 192.168.1.X, where the X is in the range of 1 to 255.