BSOD On Shut Down Three Times In Last Week.

i was shuting down my pc last week after using it all day with no problems when a blue screen appeared and the machine rebooted.I shut it down properly and it was fine the next few days . then i the same thing happened twice in a week.only on shutdown.the most recent program i installed a few weeks ago was Protools8.[code] This indicates that a system thread generated an exception which the error handler did not catch.This appears to be a typical software driver bug and is not likely to be caused by a hardware problem. The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.