Did you check the MD5 sum of the ISO file of Ubuntu? Check it once.
If it's the same as the file you downloaded, then try to make a bootable ISO using UNetbootin. Then, boot from USB. Click the "Try Ubuntu" option during booting.
If everything works, then you can try with Wubi. Wubi works on NTFS, so check the partition. If you want GRUB as boot loader you can install it from the "Try Ubuntu" window only.
I would recommend not to install in "Try Ubuntu" if you are not familiar with Ubuntu though. There may be dependencies of the Windows boot loader for a few systems. So, as I already said, if the "Try Ubuntu" method through the ISO works, then you can test with Wubi.