As someone who took six years to get anything but chickweed & crabgrass to grow in his back yard, I sympathise with your plight. In the end I had it all roto-tilled, seeded and got true-green (evil, I know, I know). I now have grass. My main issue was sandy soil & over-compacted soil. I'd tried seeding it myself for years, but to no avail.

'Luck.

-Zeke