- installed a program called speedfan444.exe 
 - didn't do any configuring - just left it running
 - when the machine locked up it was no longer visible -      DOH!
 - so I paid more attention when I'd restarted it.
 - restart temps were showing at 56 to 61 degrees C
 - when it appeared to lock up the CPUs were running      at approx 70% -temps were higher
 - I could see some fluctuations and realised I was      just about able to do things
 - So I started Windows Task Manager, and viewed      processes from all users
 - and found wmpnetwk.exe to be using 50% CPU
 - I had to kill it - service stop didn't work
 - then I disabled the service
 - restarted 
 - temperatures and CPU have been much lower      since.
 
So why did this problem appear now? Well I'd only just played with Windows Media Centre (WMC) a couple of days before. I was trying to do something with one of my customer's radio interviews; convert from wma to mp3. I thought WMC might do the trick. It didn't, but I did find an Aussie prog to do the job.
Anyway, it appears that WMPNetwk.exe was now resident in my machine and it was trying to do a lot of stuff. It may have been attempting to find details about the n thousand files it had wanted to add to its library. 
I'm not going to give it another chance. 
