Default Galaxy Tab S bootloader not accessible help!

Hi, i successfully rooted my Galaxy tab s 8.4 with the root method discussed on the development
section. I am using a stock rom. the tablet runs fine with the OS. I decided to try a custom rom.
I have tried everything to get into bootloader, the power button with the volume keys gets me to
the "downloading target the android guy logo. I do not get the screen that gives me the options
to select recovery, bootloader or reboot screen. I have all the drivers installed. fast boot fails.
I dont know what else to. I have tried loading thru TWRPa rom and i get a sig verification.
i have heard what an ADB sodeload but not sure if that will help. Any recommendations would
be appreciated.

thanks!