CiviContribute Payment Selection
I don't quite understand and am unclear whether you tried this yourself or not. I presume i don't understand, but here are a couple of factors.

1/ You should not be able to set up a Contribution Page with no options for specifying the amount.

Contribution Amounts section enabled
If you want to enable the 'Contribution Amounts section', you need to either 'Allow Other Amounts' and/or enter at least one row in the 'Fixed Contribution Amounts' table.

2/ You should not be able to set up a Contribution page without offering either Payment Processor or Pay Later

Sorry but we are not able to provide this at the moment.
A payment processor must be selected for this contribution page (contact the site administrator for assistance).