Everytime I open Lfs for a second time it just shows a black screen. Is there anyways to fix this like buying a licence or do i just have to keep re-installing the game?

I don't know what could cause that, but buying a licence will not make a difference, that's for sure.

When you say " I open Lfs for a second time it just shows a black screen.", does that mean opening it again with another running session ?

Or, does it mean that you changed the graphics to a setting your monitor doesn't support and it shows a black screen after LFS is restarted. ?

If it's the second issue, try this...

"If, for any reason, LFS ends up on the Rift in 2D mode or with a black screen, you can get it back like this :
Method 1
Press ALT+F4 to exit LFS
Delete the file "card_cfg.txt" in your LFS folder, so LFS starts up on the primary device (usually your monitor)"
http://www.vrcircle.com/post/how-to-setup-and-configure-live-for-speed-on-the-oculus-rift

I too have experienced dreaded black screen. It only happens after I unlock my S2 license and the only way to get it running is to re install and run in demo mode. I have tried the fix as explained above and still no good. This has only been happening since I installed the latest version after running a much older version for some time, any help would be much appreciated.