but when I turn on the C64 when KFF inserted, it doesn't go on the KFF menu automatically. I need to press "menu button" to see the menu of kff with files
That is normal, but the KFF normally starts the latest PRG/CRT/D64 what you last used, when you power on the C64.
You always get a blank screen, if you power on the c64? That is not normal.
No no, I got a blank screen only when the KFF is inserted. I just uploaded a video but need to e approved by some Moderator.