Yesterday I took my RPi3 and plugged it in into a different power supply - 5.0v/0.7A.
I forgot to remove my USB WIFI card and I believe it didn't had enough power to boot up as I saw no green light, so I removed the USB WIFI card and it booted up fine, then I stupidly plugged back in the WIFI card, but everything seemed to be working fine, so I used it for a while.
Another thing I did was accidentally connected 3.3v (grounded) external power supply into ONE of the GPIO pins below for about a second, I'm not sure which one:
GND, GPIO 4, GPIO 9, GPIO 11, GPIO 13 or GPIO 15
Then after about 30 minutes I moved the Pi and plugged it back in into the origin 5v/2.5a adapter, but only the red LED came up at full brightness. The green LED was blinking in high frequency, but very very dim and the Pi didn't seem to boot up (could not ping it anymore).
Today I downloaded Raspbian and wrote it to a new SD card the following way:
mkfs.msdos -F 32 /dev/sdc1 -n LABEL dd if=2017-09-07-raspbian-stretch-lite.img of=/dev/sdc1 status=progress bs=4M
Output of 'cfdisk /dev/sdc':
Device Type Size /dev/sdc1 b W95 FAT32 14.5G
Output of 'cfdisk /dev/sdc1':
Device Type Size /dev/sdc1p1 W95 FAT32 (LBA) 41,8M /dev/sdc1p2 83 Linux 1,7G Free Space 12,7G
After I tried to boot the new SD card, the RED LED stays on, but there's absolutely no activity from the GREEN LED. I have not moved to SD card prior to this incident, the slot basically had never been touched, therefor shouldn't be damaged. I tried to apply a little pressure on the card, but that made no difference.
Everything seems to be pointing that I actually burned the Pi, only thing that might point otherwise is that SD card got corrupted, therefor the weird green led pattern yesterday and after I formatted both cards, none of them work because I wrote them wrong or they're both unstable (even though they seem to be working fine on PC).
The strangest thing is that CPU is completely cold when the RED LED is on, but I'm not sure if that's normal (as it didn't boot anything and as far as I know GPU is starting the boot process).
I connected the Pi to HDMI, but getting 'No Signal' from the monitor.
Any suggestions please? Thanks!
EDIT: I validated checkums the following way, but they didn't match:
dd if=/dev/sdc1 | md5sum 775c5f915d062725f72aabeb065f3c0f md5sum 2017-09-07-raspbian-stretch-lite.img 8d9e91b1f2fc71866070dbfe823225a7
Does that mean it's written badly or am I calculating the checkums wrong? Thanks!