I have crossed paths a few times (only 5 so far) with boot sector virus infections. I would never classify myself as an expert with so few dis-infections to my name. I can tell you this - they were horrible.
No amount of deleting partitions and re-creating and then re-formatting would remove those infections. I finally resorted to DBAN (Darik's Boot and Nuke) to completely wipe the hard disk and its Boot Records. After repartitioning, re-formatting and reinstalling Windows, all was back to normal.
It was not until I was testing software programs for my category,
Best Free Partition Manager, that I realized that several of our recommended partition management packages include the functionality to work with the MBR (Master Boot Record). I have added this function to my queue for the next round of tests.
As to BIOS virus, that sounds even uglier than boot sector virus. I hope that in those cases the computer in question is one of the big name brands that offers their BIOS upgrades for download over the web. Then it may be a simple matter of flashing a new BIOS to the computer and reloading your software.