As long as the sata is not plugged in soho starts, but when the sata is plugged in ubuntu tries to start.
Bios setting is booting sata first. I run 4 Linux distros including VL7 STD Gold on 2 IDE hard drives on my Motorcycle Desktop
Shop Computer (IBM M41 I let the customers use).
I use Legacy Grub in AntiX to boot everything and just add chainload grub entries for grub 2 distros where I install grub to root instead of mbr.
Semplice, AntiX12,MacPup 529, and VL7 Std Gold run on that old clunker just fine and it uses a wireless usb for internet connection.
Since Ubuntu and VL7<at least on mine> use grub 2.
I would just make sure OS prober is installed in ubuntu
apt-cache policy os-prober
while running Ubuntu or even VL7 (if os-prober is installed in VL-7, not sure though if os-prober is even needed though so wait for other replies)
To pick up other OS installs and add them to grub 2 menu. I am not at my shop right now. The weather is just too nice for working. So I can't post my /boot/grub/menu.lst from that Desktop Computer.
Edit: Sounds like also you installed grub to mbr on both hardrives. One of the grub installs needs to be installed to /