1)
Thats a common problem with PicassoIV. If you try to use your tv modulator and connect your TV to it, I doupt it will happend.
The reason for this is for the most P4's scandoubler wich aint really stable. Especially when it gets warm.
2)
Another problem can be if you've installed AmigaOS v3.9 BoingBag2. Degrade to BoingBag1 is recommended, as BB2 aint good for Classic Amiga systems. Its rather a update for Amithlon. BB2 also crashes with my delfina.library and so on.
I hope this helps... Take Care..
AmiDelf