The single flash means a BIOs/ROM failure.  It may be corrupted.  You can try updating BIOs by pulling the next most recent version from Dell's website.  Or if you are current, then just flashing the current version.  You can't skip more than one revision at a time if you are out of date.  Or you can do the CTROL + ESCAPE on boot to enter the bios recovery screen. 
Hi all, I'm only a half step above noob level when it comes to building and modding PCs so hoping I can get some advice.  My Original PC specs: i7-8700(no k) 16GB RAM GTX 1080 460w PSU   A few weeks ago I swapped out the intel optane memory for an m.2 SSD, as well as added a SATA SSD. Also upgraded the stock RAM to 32GB (2x16GB) Corsair vengeance DDR4 RAM. Didn't really have any issues with any of that. Finally got my hands on a new GPU, the RTX 3060ti Founders edition. I knew I probably should upgrade the PSU with this card too, so I got the Corsair RMx850 (probably overkill, but figured I could always use it if I decide to upgrade to more PC in the future). I've scoured this forum and Reddit, and they were able to help me through many common problems (like getting the right power connection to the GPU_Power location).  Whenever I try to boot, it looks like the PC is booting, but the power button flashes yellow once and then turns solid blue (which I honestly can't remember if that's normal or not). But even though the power is solid blue, there is nothing being displayed on the monitor. Literally nothing at all. The same thing happens when I reinstall my 1080. The interesting thing is, if I pop the CMOS battery out for ten seconds, I can get the PC to boot with both cards. I'm currently typing this with the 3060ti installed. The PC will restart and boot fine. But if I shut it down completely it does the same thing with no display being sent. Tried HDMI and different monitors- the cords and monitors are fine. All drivers have been downloaded and up to date. The funny thing is it also doesn't show a display if I plug the display port into the MOBO port. Even tried starting it without a graphics card, still a no go. Maybe I messed with the discrete graphics settings when I disabled the intel Optane? IDK, like I said, I'm not super experienced in this so I don't know exactly how everything is interconnected. I've tried the solutions I found on other threads. I've disabled secure boot, still having the problem. I also tried to disable the Intel integrated GPU to make sure it tried to boot with the GPU, also didn't work. Only thing I've found that works is popping the CMOS battery out, and then it'll boot.  Any pros here think they can help me?
Aurora R7 GPU and PSU Upgrade