I have many problems. First of all, I had dual booted Windows with Ubuntu 19.04, then I lost my Windows. I had checked partitions with GParted, but there is nothing related to Windows.
I had checked GRUB error also. I confirmed that I had lost my Windows. But there is another issue, total space of my hard disk is 1 TB, I gave Ubuntu with 10 GB space. And there is 910 GB unallocated space in the disk partitions. I don't know where is the remaining 90 GB space.