Never remove the DVD drive!
Everything was fine until I had disassembled console and removed a DVD drive.
The PS2 does check to see if the drive has a legit disc inserted (And for some other things that need the drive to be present and closed), and some authentication may fail if the drive has been removed!
Check your drive's connection.
I connected DVD drive to the PS2 and it was working properly for short period of time but after assembly it stopped displaying image ( there's sound ). I have no clue what can cause this, I'll be glad to read your suggestion for that problem.
It's most probably the PS2's Mechacon preventing startup because it's trying to access the drive (Which isn't working properly/not connected properly).
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS