if your your pc starts and you can access to your windows session in legacy mode and not UEFI mode, so logically that would mean that your win10 Home was installed in legacy mode and not in UEFI mode. It's as simple as that.
I tested my ssd with HDTune and no errors. It strange because in Legacy mode i can use my laptop with no problem (windows starts normally) :/
It's weird. Could a dead battery and shut down the computer cause a BIOS reset and UEFI setting in it? I remember that a few months ago I installed windows in UEFI mode but ... I am not sure one hundred percent (I use many computers and I do not remember in which mode: legacy or UEFI I installed operating systems). That's why today all the time I tried to run windows in UEFI mode, because I thought I was installing the system in this mode. Could I fool myself like that?
When it was originally installed in UEFI mode, it would not have worked when it now only boots Legacy BIOS mode, so most likely you did originally install it in Legacy mode. Switching between modes will not be that easy to do on a running system.
As far as i know only a clear cmos reset the bios to default settings, in your case i am not sure what happened. What is for sure is that your windows 10 Home was installed on Legacy Mode, that's why the pc didn't start in UEFI mode.
But I checked something else. I launched Rufus to make a USB installation disk. I had two options: 1. GPT and UEFI (non CSM) 2. MBR (BIOS or UEFI-CSM) Only in the first option (UEFI - non CSM) the windows installer starts after the system restart. This is strange and indicates that I had to install windows (UEFI) in this mode
If i go by what you said in your first post, everything suggests that your win10 home was installed on Legacy mode Now to be sure whether your system is installed on legacy mode or UEFI mode do the following : go to desktop then select "this pc" then click right button then "manage" then select "disk management" if you see 100 MB partition named "EFI partition system", it means that your win10 home was installed on UEFI mode (either pure UEFI or UEFI with CSM enabled). A screen will be more than welcome.
Just my 2cts: CMOS RAM is mostly backed by the main battery in modern Laptops. You almost drained it, so, something in the UEFI firmware got messed up, possibly the checksum. In case of a faulty checksum, the UEFI firmware resets all its settings to default. Looks like the Windows was installed earlier with Legacy setting, but the default setting is UEFI, and the reset set it back to that.
If windows only boots in legacy mode, it would seem it was originally installed in legacy mode. Why not just reset the firmware to boot legacy instead of UEFI, and be done with it?
I'm having almost same problem, but after force shutdown (also bios mode didn't changed when this happening) When the laptop has completed booting, after using for a while suddenly it freezed (and also sometimes followed by bsod), rebooted by itself and no bootable device appearing indicating SSD was dead. But after restarting laptop again, it booted normally to system (also SSD is still deteced in bios) and it worked normally until force turn off again My laptop model acer aspire E14 (E5-411G), ssd Adata SU650. Windows is installed on UEFI mode. Already tried installing linux (last time was manjaro), it freezed also after force shutdown and booted into linux No errors in SSD. That problem will occured again after force shutdown. Don't know if that was SSD problem I'm using even no errors found (I had replaced once after bought that SSD model a year ago, 2 days after using it suddenly not detected anymore and got new one with same model) This problem just happened again 4 days ago, using hibernation mode causes my laptop to do a full reboot when I resumed it as the laptop has been forced shutdown. It freezed and rebooting with no bootable device appearing after using for a while (also l'm leaving my laptop for a while after windows finished booting, got greeted again by no bootable device screen when I'm returned just to use my laptop again) Maybe any thoughs beside of bad SSD/HDD?