Maybe this MorphOS freezing is connected with situation I write below?

Sometimes I have problems with booting MorphOS. I see only a black screen. Than I must turn down my Amiga and try to start system again. And when I don't have a lucky day ;) I must turn down and turn up my computer even 10 times to see the MorphOS...

But sometimes I turn up my Amiga and MorphOS is booting for the first time.

Somebody have any ideas why I have this problem?