Hello T Suominen,
Thank you for keeping us updated about the issue.
As per the description which you have provided in your post, I would suggest you to try the steps provided in the following Microsoft article and see if it helps.
Event ID 512 — Shadow Copy System Writer Functionality
http://technet.microsoft.com/en-us/library/dd363857(v=ws.10).aspx
Hope this would help. If issue still persists post back with current status of your computer and result of proposed suggestion, we will be happy to assist you.
Thank you.