Booting Windows when early boot fails

So this was my problem; an old laptop wouldn't boot Windows XP. After the Grub menu, I would just get a black screen with a blinking cursor when choosing Windows XP. Other installed OSes worked fine.

Ntldr, Ntdetect and boot.ini were all fine. Reinstalling the MBR (running fixmbr or fdisk /mbr, deleting Grub) or running Windows repair would not fix it. Also the boot flag was set.

Turns out the partition itself, not just the disk, has a boot sector, this was probably corrupt. I got it to boot by using Grub, and replacing the line "chainloader +1" with "ntldr /ntldr" in the menu entry. This skips the boot sector on the partition and loads ntldr directly. Wehey, it booted!

Fixing Windows XP MBR without the install CD

I just had a mishap with a failed Ubuntu install (GRUB failing due to the BIOS having problems with large drives) on a laptop and needed to boot back into XP. "Normally" (or rather, in the past) the XP install CD would do the trick, but because the laptop has a SATA drive the install CD couldn't find any disks.

I could possibly have made a custom install CD (the laptop doesn't have a floppy drive for the SATA drivers the install CD needs) but an easier solution was the great SystemRescueCD. This is completely free and works well.

I booted the included FreeDOS image, typed fdisk at the FreeDOS prompt, selected my XP partition, and hey presto, a rebuild MBR option!

So there you have it, free MBR repair without the dodgy XP install CD. As I didn't find this by Googling for a solution I'm posting it here hoping it will help others in the same pinch.