What... is this?!?!

So, I own my own business and when I took over a couple of months ago I decided to set up a network so that my graphic artist and embroiderer could each have their own machine and be able to transfer files back and forth. I came in today and powered on one of the machines and when the desktop came up, I immediatey got an error saying "Automatic Updates has encountered an error and needs to close"… so I did a system wipe and restore, and viola… no prob. But now… the machine that my embroiderer uses can no longer access the internet, and I'm also getting an error box that says "Windows Security Center Notification App has encountered an error…" This seems like less of a coincidence (because Automatic Updates and Security Center are related) and more of a virus bouncing around in my computer. So far, I've ran Avast! anti-virus software (hey, it was free anyways lol) but could not d/l the spyware database for Spybot, and Ad-Aware crashes right after I double-click on the install file. The network settings are fine as actually, my file and printer sharaing capabilities are unaffected… I'm completely lost here. Any ideas? Format maybe?

First, create a new folder on your desktop with a memorable name such as 'HijackThis'. Next, download HijackThis (scroll down the page to the 'HijackThis Quick Start' header) and unzip it to the new folder you just created. Make sure you unzip it, don't run it from the zip folder as it will not make proper backups if we need to fix anything.
Next, run HijackThis and click Do a system scan and save a logfile.
When the file opens, copy the entire contents by holding down Ctrl and pressing the 'A' key at the same time. Open a reply to this thread and paste the log into the reply by holding down the Ctrl button and 'V' at the same time.

Do that for each computer that is experiencing a problem.