I have a number of divx convertors but just recently they all seem to crash half way through converting, I have tried new codecs and rolled it back. Any one have any ideas what it could be?

There has been no updates that I can think of, the software runs for a few minutes and then my machine just restarts. I have trawled everywhere for an answer but no one knows why.

Have you installed any of those CODEC packs?   Those types of packs are riddled with problems and whenever you are having issues, they should be the first thing uninstalled. 

What may be happening, is that you have some conflicting CODECS. 

Check your Device Manager to see what CODECS you have, and take a screenshot of it and post back here.  They are listed under your "Sound, Video and Game Controllers" in Device Manager (to get to device manager, click Start, then Run, then type:  devmgmt.msc  then hit enter).  Expand the "Sound, Video and Game Controllers" by clicking on the '+' , then double click on "Video Codecs".  then click on Properties.  This is the Video Codecs you have installed on your pc.  Take a screenshot of them (if you have a lot of codecs listed you may need a few screenshots, to capture them all) and post back here and we will look for any potential conflicts.

As an example, Here is a screenshot of mine,

Hi Bluefoot I'm afraid I can't make out the screen shot could you upload it to imageshack full size and post the link here

Bluefoot - you'll get a better result if you use Alt+Print Screen. The capture will then be the active window instead of the whole desktop. Make sure that the dialogue box you want an image of is the last thing selected then use Alt+Print Screen.

I could be going blind but I don't actually see any divx codecs on there could that be your problem?