Disconnect your working drive(s) then install a spare drive, a device with nothing valuable on it, on SATA0, typically the system default primary boot device location. If you're like 99% of the Hackintosh community you have a spare drive lying idle in a drawer or toolbox, if not you ought to own one. You can buy a new 256GB SSD from Amazon for under $40 USD. You can buy something pre-owned and risky on eBay for much less, but I advise again that. There's no point going to the trouble of conducting a hardware test using an untrustworthy apparatus.
What you're going to do is install an OS on that spare drive to ensure that your MB is 100% good. I recommend using some flavor of Debian Linux such as Ubuntu or elementaryOS since they're free and readily available. Or you can use MS Windows if available. It doesn't matter. Once installed and running apparently normally, do some stress testing. There are many free-to-use stress-test applications out there. I suspect your MB, CPU, and RAM will pass these tests because I also suspect the EFI partition on your production High Sierra SSD is hosed in some way.
Something else that many Hackintoshers find useful is one of these:
To my mind drive docks like this are better than single-cable SATA/USB adapters because one needn't worry about powering the drive. Not necessary, but useful.
Assuming 100% functionality of your MB, CPU, GPU, RAM, etc. as demonstrated by your test configuration the next step is to repair the EFI partition on the production High Sierra SSD. Using
TonyMac's High Sierra guide install macOS 10.13 on the test drive. Don't bother to preserve the OS you installed on it beforehand. It was just for testing only. Once that's up and running you can mount your non-bootable production SSD, and here's where a SATA-to-USB dock comes in really handy. Using
this guide mount the EFI partitions of each drive. Be sure to mount the test drive's EFI first so that you know that is the good one because both EFI icons will look identical on the desktop. Copy the data from the problematic EFI to a thumb drive to save it. Then replace the data with the data from the test drive's EFI partition.
Power off. Disconnect the test drive. Re-install the production SSD. Reboot with fingers crossed.
