Thanks for the reply.
Not sure now what's going on. Computer doesn't crash holding down shift key, but no disc is recognised in the drive the LED does flash to indicate it is reading the disc, then goes off after a few seconds, this is normal, and at this point other discs are recognised. I have Pioneer DVR 108 and DVR 110 and have the same problem in both. Could it be the DVD drives that's the problem? They both worked fine before EMC8, so I just assumed it was that. Maybe I was wrong.