You neglected the possibility of Disk errors. THAT was my 100% I/O problem which has now been solved.
I repeat here -
Well, I don't know about Skype or Chrome - neither are on my (previously faulty) desktop, but my 100% disk slowdown problem has finally been solved! It was a failing disk drive!
It is advisable to have SMART enabled in the BIOS, and a good hardware monitor installed, such as ***SPEEDFAN***.
For details please see my MS Technet response
Now, I have to go shopping for a new HD. I suspect it will not be a Western Digital this time!