All of this is speculation from my experience modding my Area 51 R5; I don't think the missing temp sensor will prevent a successful POST. It did however cause my case fans to run 'full tilt'. If the 2 fans you are referencing on the IO board are the U2/SSD cooling fans inside the mounting bracket . . . I don't think those missing would prevent a successful POST. When I did not have a full complement of OEM case fans, I got no response from the monitor (black screen); periodic beeps (maybe 2 min apart), and it seemed like it was cycling through diagnostic testing for OEM case fans. This is complete speculation because I have no monitor video. If you think the OEM case fans will help . . . PM me how many you need, and a good shipping address.
Hello I have the R7 motherboard out of the case on a bench. Original Power supply. Setup: The issue is that the board does not POST. No video out. To my mind it is in some type of loop (keyboard when connected, the num lock repeatedly  goes on and off for about 5 seconds in time with the GPU fan coming on and off (video link:[URL] The logo board LEDs are a cyan color if that is any indication. There are no beeps, so no indication there either I have tried with multiple GPUs (the 8570 is known good), multiple sticks of ram in all of the slots by itself, and everything I can think of. I have also cleared the CMOS, and bled power in case that was the issue, but no beans. I have had the GPU in different PCIE slots. I removed and reseated the CPU. I double and triple checked each connector/connection. The behavior is unaffected by any of these things. No matter what I do, it does that 5 second loop. Any guidance on what I might be missing or what else I can try? Thanks pvravi1
Area-51 R7, motherboard no POST