You are correct that the boot sequence does not activate till after the POST or after you exit the bios setup.
Are you able to get into the bios setup at all after pressing <Delete> during the POST?
If not, then try <ALT> + <F2> during the POST.
If you have any reason to suspect that any of the jumpers on the motherboard have been tampered with since you left it on your shelf, then you might like to make sure they are all correctly located in their default position.
Another thing to check since the processor has probably been off and on the board a few times during this process, is to make sure none of its pins inadvertently became bent.