1. Insert the Ubuntu installation CD.
2. Restart the computer.

3. Change the boot device to CD/DVD-ROM from the system BIOS or by accessing the boot device menu. Your computer specifies how to access the BIOS or boot device menu at the bottom of the screen upon powering on.
4. Save the boot settings and restart.
5. Select 'Try Ubuntu without any change to your computer.' This launches Ubuntu in Live CD mode.
6. Launch Terminal by selecting 'Applications,' 'Accessories' and then 'Terminal.'
7. Type 'sudo grub' and then press 'Enter.'
8. Type 'root (hd0,0)' and then press 'Enter.' If GRUB was installed onto a different hard drive or partition, you must edit 'hd0,0' to reflect the hard drive that contains GRUB. Be sure that these changes are reflected in Step 9 as well.
9. Type 'setup (hd0)' and then press 'Enter.'
10. Type 'exit' and then press 'Enter.' GRUB is now reinstalled and the error should be resolved when you restart your computer.