DC with IDE and no GDROM will not boot

[Some chump]

Hello.

I have added to my DC an IDE HDD and a dual bios.
The bios is flashed with "boot_loader_unlock_G1_IGR_dbs_nogdrom.bios"
DC will boot to dreamshell on the HDD and games load fine.

I installed a 33.8688MHz oscillator to B23 of the GDROM connector and removed the GDROM. When booting the DC will freeze in the "Dreamshell Boot Loader v2.3" menu.

So, with the GDROM attached, DC boots to IDE HDD.
With GDROM removed and 33.8688MHz oscillator attached and ".nogdrom bios" installed, DC will not boot.

Is there something else I need to do to boot to IDE HDD without the GDROM fitted?