Can't get into DiskMode / DFU but HDD and flex working

Hi everyone

My beloved iPod classic photo got broken

I've tried to fix it but no success, here is what I find out:

- I know HDD and flex ribbon are 100% working - as I transfer them to other iPod photo and they worked.

- HDD is detected in Diagnostic Menu and successfully passes Scan Test

- When choose Diskmode from Diagnostic Menu - iPod stuck at NOT light up Apple logo

- When normal boot - it stuck at lighted up Apple logo

- Can't do DFU - it is switching off - booting - switching off and.... booting automatically (doesn't remain switched off)

- It is slow ("drawing") in Diagnostic Menu compare with other iPod photo

- It is passing all Memory tests in Diagnostic Menu

- iTunes not recognise it