grub err 17 for linux , grub err 21 for windows
 

I installed ubuntu 9.04 on my external hard disk. When i try to boot from it i am getting an error grob loading.. grub error 17. I am using an ibm thinkpad which has windows installed in it. After installing ubuntu when i tried to use windows (with or without the hard disk attached) i got grub error 21. My last resort is to restore my thinkpad to its factory settings(i will lose data!!) and format my hard disk and try to install ubuntu again. I really want to avoid that. Please help!

When you installed Ubuntu to the external, where did you install Grub? The root partition on the external? master boot record of the external? master boot record of the internal?

Grub Error 17:
Grub Error 21:
Can you load the Ubuntu install CD and open a terminal and run the command: sudo fdisk -l (lower case letter L) and post partition info here?

Which version of windows are you using?

grub err 17 , grub err 21 solved
 

Thank you Yancek for replying. I did the following and it worked.
For grub err 21, i used a Windows xp cd and ran the fixmbr command from the recovery console. This allowed me to boot to windows.
For grub err 17, i installed ubuntu again on the external hard disk. To resolve any conflicts between the two hard disks i physically removed the internal hard disk before installing ubuntu on the external.
This worked and now i have both ubuntu and windows running well.
Thank you again, for your time.