This sounds like the 2 occasions that I encountered something similar...

1. I had a motherboard that would refused to mine under windows, once I launch Claymore, it would simply crash. Using ethOS, it worked like a charm. It is an older motherboard so it could be chipset related.
2. I had a version of Crimson drivers that were not bios mod friendly. Check to ensure you have a bios mod friendly version (posted in my article) or use the patch in this article (https://www.monitortests.com/forum/Thread-AMD-ATI-Pixel-Clock-Patcher).

Good luck!