Hello Icyhot, welcome to the Place!
From your other post, it appears you are using 3 different PS2 models across 4 different units:
PS2 Fat (30001)
PS2 Fat (39001)
Two PS2 slim (70012)
So, you will definitely have to be more specific and give lots of details...
The more the better so I can help you, please.

Dont be shy, I will read the whole post even if it is a book lol... Seriously, I will.
Especially, please note the version of FreeMCBoot you are using, your exact model used during each test, specifically what happens when you turn on the PS2-unit with your FMCB memory card inserted, what happens when you do the same with it NOT-inserted, any modchips installed, any factory-seals broken, Et Cetera (...and other similar things...).
If it boots to the Browser Menu with the card inserted, please list ALL the available-listed-options that appear on-screen in that menu.
Hopefully, we can sort this out for you soon.
Again, welcome to the site!!!
-Uni