Help! clear cmos not clearing on z390 extreme4

Subject line says it all. New build was running fine in Win10 until I tried to set up Thunderbolt with Asus Thunderbolt 3 card installed. Made bios changes for Thunderbolt and that's all she wrote. When powered on the fans all start up but nothing else, no beep codes and no video, no bios screen, no Windows. System then reboots itself twice and then just sits there with fans running. I've tried numerous times clearing cmos. Tried removing coin battery for extended periods (like, days), jumperiing the clear cmos pins with battery removed. PSU turned off and unplugged each time. Even tried pulling the big ATX power connector from motherboard. No change. So how can I get this Mobo fixed or replaced?

Thanks for you advice.

I'm giving it 1 more try using your sticky instructions, on the chance that my not doing the steps in the right sequence or duration may have been the issue. I'm waiting the max 4 hours you suggested, ~2:00 hrs to go as I send this.

To answer your question, no I didn't pull the TB card, this time. However, I previously tried pulling it and going through cmos reset several times. May I also point out that the machine was working fine with the TB card inserted (but not connected to a TB device) before everything went black. What killed it was apparently my attempt to set the TB options in the mobo bios.

As far as pulling everything, I've unplugged all external cables (mouse, kbd, HDMI, power--and shut the PSU switch off, I pulled the LAN cable days ago and have left it out since) every time.

Also please note this board came with only 2 CLRCMOS pins and no jumper cap. So I purchased some, and assume that jumping the 2 pins is the same as positioning the jumper provided in the 3-pin configuration into the clear position and removing the jumper is equivalent to repositioning the jumper with 3-pin. I'm providing these details in case any of them are significant.

FYI, I was told by an expert who builds PC's for musicians and recording studios that the Asus TB board would work with the z390 extreme4 so I'm skeptical about that being the cause of this. Why would a PCIe card prevent cmos reset? Or scramble the bios so it can't be reset? Once again, I emphasize the TB card was plugged in from the beginning when this machine worked fine, except the TB connection didn't work and I was trying to find the right bios settings for it.