Reseted the CMOS....opencore not booting shows only blinking dash

I had installed High Sierra on my built with opencore. It was fully functional and I was using it. But yesterday I reset my CMOS and from then the system won't boot. Windows 7 which is on other drive boots fine. But when I select the usb drive to boot it just shows a blinking dash on top left corner. My built: CPU core 2 duo e7200 GPU gt 710 Ram 4gb ddr3

Please help