I have downloaded GhostBSD 21.05.11 from official website using torrent link . I wrote ISO to 8GB USB flash drive using balena Etcher on a windows 10 machine . When I try to boot from that USB drive it take like 3 seconds and boots to OS installed on hard drive .

I have tried this using two different USB drives and two computers but the result remained the same .

When I wrote ISO using Live Linux USB upon booting it just gives black screen .

Please help as I eagerly want to use GhostBSD.

Thank You

All I can offer is how I did It. ISO from same source as you. I have MX Linux 19.04 on another laptop on my desk. MX Linux USB maker on board took care of ISO to Kingston 16GB flash/thumb drive. On this laptop, Dell Inspiron 3737 that had win7 on it previously, I tapped F2 on boot to get into bios. Made sure Secure Boot was disabled,made sure Lagacy Boot was enabled and UEFI disabled.
Next,I re-booted tapping F12. The flash drive was listed there. I chose the flash drive and install of GhostBSD began,blowing out win7 and all is well.