Hello, I'm using a Raspberry Pi 3 model B and I just installed Raspbian Stretch. Whenever I turn on the power, the system is not booting, all I can see is a picture of Raspberry fruits and a cursor blinking. I can type here, but cannot login.
If you expanded the partition by gparted or other tools instead the raspi configuration tool it may cause the problem. Flash again the image in the sd card, and let only modify the partition size by the config tool. I took the answere from here http://www.zdnet.com/article/hands-on-with-raspbian-gnulinux-stretch-for-raspberry-pi/
Just a thought.
Many a time, owners of a Rpi just cuts the power cord to the Rpi to turn it off. This will cause both the boot and rootfs partition on to (micro)SD or USB memory stick to become corrupted. To recover from such a filesystem corruption, insert the Rpi (micro)SD or USB memory stick to a Linux desktop computer and run dosfsck -aw /dev/sdX1 (boot partition) and fsck -fy /dev/sdX2 (rootfs partition) (where X is the device ID, i.e. /dev/sdb1 or /dev/sdc1, etc.) to clean both the corrupted partitions. Then, plug back the (micro)SD or USB memory stick to the Rpi to see if it will boot OK.