Failed to enter windows

Hi everyone,
  After installing ubuntu, I can not get into the windows and struggle with a bios loop, and failed to repair it with iso  or other startup disks. Gently ask if there is any possiblility I can repair the  Windows reserving documents in C.
System  information :
MB : B350M MORTAR (MS-7A37)
CPU: AMD RYZEN 7 1700X EIGHT CORE PROCESSOR
RAM 32768MB
BIOS E7A37AMS.170