blank screen

Bought a second hand DS-7216HGHI-SH. Was told that just power adapter is missing. I have added regular 12V DC socket in parallel, so I can use standard 12V connector. In process I have noticed that all four 470u/10V caps were swollen, so replaced all caps just in case. On board battery CR-1220...

I changed the video setting from NTSC to PAL and now the screen is blank. I removed the battery turned it on and off then replaced the battery. I hit the reset button on the board. I held the stop button and a combination of the above. How do i reset back to factory?