I have had zero experience with 100% disk usage (obviously my experience is not the only one but I have had quite a bit of experience with multiple deployments of Windows 8 / 8.1 and have never really encountered this) but there are a few things that you could try. There are so many different part configurations under the sun that it can be hard something to troubleshoot so hopefully it goes well.
I found this thread that seemed to help quite a few people. I also performed most SSD management setup recommendations. Disabling defrag, pre fetch, super fetch, etc. Windows 8 does quite a bit of this by default but there are still things that you need to manually set. Are you using a SSD or a regular HDD? Perhaps there is something wrong with the drive? Either way, maybe take a look through this thread and see if anything helps.
http://www.tomshardware.com/answers/id-2027511/windows-disk-usage-100-problem.html