Freezing after bios installation

[lolof]

Normaly, you should have a physical switch somewhere on the case or maybe inside the case.
This switch has to be used to choose on the bios you want to boot in.
You have to find this switch and toogle it and after your dc will boot in the original bios.
For this operation you do not need the dreamshell disc, you will need it if you want to flash the bios in the second chip, the one who is soldered on the original one.
If you cannot find the switch, you should open the dreamcast and look for the extra chip or the switch.