I've experienced this exact issue multiple times. Windows is freezing because a drive is not responding (either the cache disk or one of the HDDs, though it sounds like it might be the cache disk if things work fine when you don't have it).
First, make sure you have the latest IntelRST drivers installed. There was a bug about 1-1.5 years ago which would cause the driver to think a drive was bad when it really wasn't, and kick it out of the array, which has since been fixed.
Second, turn everything on and enable SSD caching again. When it freezes, wait for the system to recover. This may take 5-10 minutes. (I can't remember, but I think the default values are a 60 second timeout and 10 retries before disks gets marked as failed; 20 minutes is too long, go ahead and force an unexpected reboot if it locks up that long).
After the system recovers, you should be able to open up the IntelRST control panel and see what drive it rejected from the array (one of the RAID 0 drives, or the cache drive). There's a decent chance that drive is dying.
I had this exact behavior when my SSD was dying and I was using it as a cache drive. Hybrid caching is rough on an SSD, and I had one of the early models that didn't handle high write cycles very well. It took forever for me to figure out because after the SSD failed, it would seem to work fine as a standalone disk for a while, but after a few months it stopped showing up in Windows at all, even other systems.