Not being able to get into bios or your OS sometimes would suggest 2 things;
# Your MBR has become hard to read - assuming you have an MBR disk.
# Your bios is becoming hard to read
I would start by running these commands if you can get a CMD prompt open. NOTE: They may take a long time to complete - like hours if it is real bad.
***chkdsk c: /f*** This will check your disk for errors
***SFC /scannow*** This will check your system files
These will do things SFC can't
***DISM /Online /Cleanup-Image /CheckHealth***
***DISM /Online /Cleanup-Image /ScanHealth***
***DISM /Online /Cleanup-Image /RestoreHealth***
If none of that helps, try to create an image if you can get it booted up. Macrium Reflect Free is my go to program.
It may or may not work depending on it being able to read that MBR and the rest of the disk. If it does not work at first keep trying as it will reduce the pain if other things don't work. If you have just a C: drive, this will also provide a backup of all your stuff. If you have more than one partition on the hard drive, image the other partitions separately.
Then I would try to rewrite the MBR - this is the short answer but you can search for longer answers
To rewrite an MBR (Master Boot Record), you can use the "bootrec" command in the Windows recovery environment, accessible through a boot disk or recovery USB, by navigating to the Command Prompt and typing commands like "bootrec /FixMbr" to repair the MBR on the selected disk; this process is typically used when the MBR is corrupted and needs to be overwritten with a fresh copy.
If that doesn't work, and you successfully created an image, try to restore it.
If that doesn't work, replace the hard drive and restore the image to the new drive. If you have other partition images, restore those also.