How to disable FreeBSD boot loader?

[Turquoise88]

Hey, thanks for your previous answer. I will reply to them later. I have been busy.
I have a new problem. I have to disable or remove the FreeBSD Boot Manager because I can't boot Windows XP now. I get an error message when I'm trying to boot Windows (by pressing F1=Win at the OS selection): "Disk reading error. Press Ctrl-Alt-Del to reboot."
The rebooting doesn't help. I'm back again in the loader. FreeBSD works very well. FreeBSD version is 7.2/AMD64.

[s0xxx]

Well I will not tell you that you nuked your Windows partition as I don't know what you did, but it seams as a serious error. Anyway, follow this to get the Windows loader back, and also use it to boot FreeBSD with it:

First you save the MBR in case something goes wrong so you could restore it and at least boot the FreeBSD. I also suggest you get the fdisk and bsdlabel output to a file on a usb disk so you have other needed information in case of failure.

dd if=/dev/ad0 of=/mnt/usb_disk/mbr.backup bs=512 count=1

Then you need first sector of your FreeBSD root partition. You will put this on Windows C partition so NT loader so can pass instructions to it. It is actually /boot/boot1 (stage one) so you could copy it from either FreeBSD root partition (unless FreeBSD is on another disk), install CD, or just grab it with dd:

dd if=/dev/ad0s2a of=/mnt/usb_disk/bootsect.bsd bs=512 count=1

This is assuming your FreeBSD is installed on second slice of the first disk. Then, you boot the Windows installation disk and go to recovery console and just type:

C:WINDOWS> FIXMBR C:

This will restore the NTLoader back. Try to see if you can boot into Windows now. If it doesn't boot, go boot the CD again and try the FIXBOOT command.
If it boots, open boot.ini file located in C: and put the following bellow the line mentioning Windows (you do not delete anything, just add another entry at the end of file):

C:bootsect.bsd="FreeBSD 7.0"

That should present you with an option to boot FreeBSD after reboot. If you ever deceide to remove FreeBSD you just delete the file and remove the entry in boot.ini.

[Beastie]

It's possible the partition table is damaged (more precisely the C/H/S values for the Windows partition).
Resetting the boot manager (MBR) code will probably not change anything.

Since you can boot FreeBSD, do a backup of your current MBR as s0xxx suggested.

Now, edit your partition table using # fdisk -u ad0

Say no to the first question ("what the BIOS thinks").

When it says "The data for partition 1 is" (Windows being on partition 1), press y to change it.

Press enter 3 times to accept the defaults.

When it asks for "Explicitly specifying beg/end address", press y, give it a 0 (zero) for each of the 6 subsequent questions (beg C/H/S & end C/H/S) and say you're "happy with this entry". Even though you already backed up your MBR, you could also write down the values you just zeroed here and restore them later following the same process if this doesn't fix the problem.

When it asks for changing other partitions say no.

In the end, tell it you want to "write the new partition table".