How is it possible for a machine that has been running without interruption for the last 114 days, to suddenly do -35million points one day? My rank hasn't changed, just the total for this one machine which has had no modifications of any sort for four months, it's absurd!

The project server probably changed the computer's ID number, or created a new computer ID, or merged the computer with a different one. Any of which could confuse the BAM stats.

It's also possible that the computer account was deleted or banned by the project.

You should log in to the project web site and check your computers list there to see what happened.