I've done numerous scans, no malware at all, I've defragmented the drives, disc clean-up, system refresh, factory settings reset, read loads of posts on this, increased/decreased virtual memory, analysed PC and everything seems fine. I just don't know what else to do.
It shows the 100% disc usage on just a small 1 mb/s but sometimes 30 mb/s, the thing causing the most data/s is sometimes "System", but I cant find out what exactly. Disabling firewall and all antivirus programs didn't help.
Launch Windows' built-in Resource Monitor tool and go to Disk tab. There you'll see a lot of your disk-related activity. You'll be able to see what files are being read/written to, what applications are doing that, which disks are active and a lot of other useful information. It will help you figure what exactly that "System" process is doing.
I had seen this issue when Windows 8 beta was released and again when Windows Blue which is Windows 8.1 which is now available that it had the same disk driver issue. If you install the latest disk driver for your machine by going to the manufacturer's website and downloading and installing one that is compatible with your Windows 8 or 8.1 machine that should solve your 100% disc speed issue. If you look in your task manager you will only see that the system process seems to be causing the majority of the disk activity. This is due to the SATA driver not interpreting your device correctly. It is also likely that not only are you using a SATA device but that the device is a stack of magnetic spinning disks rather than a solid state drive since this issue doesn't occur with solid state drives and only with regular HDDs (Hard Disc Drives).
Please chk this one out from microsoft:
