How debugging KVM

Hello,

I got several VM under KVM freezing at startup without anything in log and qm report vm started (then internal error)
On console i only have a cursor and bios never start.

Adding another disk and changing boot order on it fix the issue but need copy file and reinstall all program (windows vm)
So it's not a config issue, it's a problem on the VM disk.
I use RAW disk. Happen already 3 times.

How i can debug it for find where the problem happen ?
Why even BIOS not start ?

Thanks for help.