I installed FreeBSD on my Toshiba laptop and now I can't access Windows on the laptop. How do I undo this mistake?
The BIOS is not involved here; the bootloader is where the problem is coming from (if someone with the appropriate powers could change the subject, that would be helpful). This would have been easier to take care of on the technical support mailing list, because there isn't enough information in the report to figure out what has gone wrong here. The first step in looking at the problem will be to determine whether the disk is using an old-style "MBR" partitioning or a newer "GPT" partitioning. This can be determined from the gpart(8) command, "gpart show /dev/<whatever device your disk is>". The second step is to make sure that the Windows partition is still present. That should also be present in the output from "gpart show". Assuming that you have an MBR-partitioned disk, the third step is to reinstall the bootloader and configure it to show all partitions. See the FreeBSD Handbook section on bootloaders to be sure, but I think the command would be "boot0cfg -B -m 0xf".
I've seen this in my system as well. It's not the BIOS (we can't simply overwrite that) but your boot partition. If ypu were careful during the partition phase it is also possible that your Windows boot partition is still there but inactive. I have had luck rescuing such systems with the Windows repair disk and even FreeBSD. Another helpful tool for dual booting is EasyBCD. I will be closing this PR, hopefully you found a solution since 2014.