You'll need to enter the BIOS settings to be able to choose default settings. So that's a problem if you can't.
All you can do: find out how to reset the BIOS hardware-wise. That could be a jumper on the motherboard. Or disconnect from the net and remove the battery for a minute.
Still, it's not clear from your post why you entered the BIOS to start with, and why you think that invalid BIOS-settings are the cause of your current problems. After all, even a badly configured BIOS should put it's name and version on the monitor before doing anything.
For me, this could just as well be broken hardware. Do you hear any beeps? Some beep patterns point to well-defined errors (like: no working RAM found).
I'm not sure what I did to tne Bios settings but now the PC won't go to post and I can't get back to th Bios settings. The monitor won't even display anything anymore. HELP