OK, try this for a messy hack ...
1) unplug the HDD and go into BIOS
2) in BIOS, for boot device priority choose CD/DVD, and make sure that booting from the hard drive is actually DISABLED, and that boot from another device/search for bootable devices/whatever it's called in your BIOS is also DISABLED
3) shut down, put HDD back in, and try to boot from your CD
4) TRASH the system partition if it works -- just delete it.
Then reenable booting from the HDD and reinstall and blablabla