Does this happen when you play DVD Movies only, or even when playing files from harddrive? I used to have problem way back when I used PowerDVD, I eventually found out the reason was that my DVD wasn't running in DMA mode.
If this is intermittent crashes that started happen out of nowhere, it could be caused by anything from a bad memory to a bad powersupply. But since you mention PowerDVD and Nero it could be related to the DMA thing as they remind me of the problems I had. Check the current transfer mode of the ide channels the cd/dvds are connected to in your cpanel->system->hardware->device manager, if they are in PIO you are in trouble.
If this is intermittent crashes that started happen out of nowhere, it could be caused by anything from a bad memory to a bad powersupply. But since you mention PowerDVD and Nero it could be related to the DMA thing as they remind me of the problems I had. Check the current transfer mode of the ide channels the cd/dvds are connected to in your cpanel->system->hardware->device manager, if they are in PIO you are in trouble.