booting from USB hard drive on lenovo u350

I have a lenovo ideapad u350 with external USB DVD drive and HDD (Samsung) (I do not want to overwrite the internal hard drive which has wondows 7)
While booting from the DVD drive with OpenSuse 11.2, the booting is erratic. Once in a while it just hangs (especially if I reboot from windows without powering off the laptop)
On one of the hangs (with fresh power on), the last thing displayed was:
b43-pci-bridge 0000:03:00.0 PCI INT A -> Link[LINKB] -> GSI 11 (level, low) -> IRQ 11

In any case, I was able to install when it booted successfully onto my external HDD. But, the MBR was changed on the internal drive (to point to grub loader on the external drive, I suspect, as I had to select windows from the grub options to boot windows.). This had the bad side effect that I could not load windows if I disconnect the external HDD. So, I restored the windows 7 MBR on the internal HDD.

To put a new MBR on the USB drive, I wanted to boot the DVD and go to repair installation. But, this consistently refuses to recognize the external HDD. Any ideas on how I can fix this?