I am sorry you are having problems with the system but let me help you.
It is important to say that since this motherboard is a mature product, the latest drivers we have for this unit are for win 7 64 bit.
Now, since it is discontinued product, it is possible that using newer SSD on the unit you may encounter compatibility issues. You can try it or maybe another user can provide feedback on this matter.
I'm surprised more people haven't written asking about this same idea: upgrade a DP55KG system to Windows 8.1 (64-bit). Even though it's discontinued, it's a pretty awesome motherboard and you'd have to spend a pretty penny to get something comparable in a new board (with new processor, new ram, etc.). Really, about the only thing you'd gain with a new system is 6.0 SATA.
Anyway, I've just done this upgrade. I took an existing system with Win7 (x64) and did a fresh install (not an upgrade) with Win 8.1 Pro (x64). I ran into driver problems with two features: the infrared (CIR) and the RAID. A search around the Net found the right CIR driver on the Asrock web site, so that's taken care of. The RAID situation is more curious.
I have a 500 GB SSD for my system drive and then a mirrored pair under RAID. The Intel Rapid Storage Technology app installed properly and it all seems to work fine. However, in Device Manager it shows no driver installed for the RAID device. It says it can find a driver, but can't install it. As I said, everything seems to be working fine, so I'm not sure if there is any importance to that missing driver. What do you think?
The RAID Driver is the Intel® Rapid Storage Technology driver you install. I recommend you reinstalling the ME driver and the Chipset driver. Besides these drivers, you can try installing the Intel® Rapid Storage Technology if you do not have it installed.
If it is working just fine means that all drivers have been installed and the system may not be recognizing a different device.