This wouldn't happen to be an efi system? Maybe this will help since ZorinOs is ubuntu based,
https://help.ubuntu.com/community/Boot-Repair

Hi John

Yes I have tried the up and down arrows as you suggest but it doesn't do anything apart from booting directly into Zorin. I see the following post by Colourpurple is suggesting a boot repair disk based on Ubuntu. I might give that ago. I really appreciate all the assistance given by everyone

---------- Post added 01-20-14 at 04:13 PM ----------

Thank you Colourpurple......I will give this a go

The default for Grub2 is NOT to display the menu. However, if more than one operating system is detected as in your case, the menu should display. Some things you can try to see if you can boot xp media center. When you see the black screen after the BIOS, hit the Shift key. If that doesn't do anything you can check to see if you can boot xp. Since your grub.cfg file shows the xp media center as the seventh menuentry option, when you see the black screen, hit the down arrow on your keyboard, carefully counting 6 times which should take you to the xp entry. Hit the Enter key. I had a black screen on an install and tried this once and it worked.

The link below at the Ubuntu forums (post #2) explains in some detail the use of the Timeout options in Grub2.
At the same link, in post #4, there is another link to a page which explains in some detail the Timed display and Hidden options.

Thanks Yancek......Nothing worked unfortunately so I have made the decision to forgo the dual boot option and install Zorin as the sole operating system because apart from the dual boot failure......I am very happy with it. I would sincerely like to thank all forum members who have tried to help me and to each of you, you must be as frustrated as me that we couldn't resolve the issue but thank you for your persistence. This is a great forum and I will continue to use it and you never know as my knowledge increases I might be able to make a contribution Thank you all.

Just realized I forgot to post the link yesterday. If you haven't removed your xp yet, you might give it a look.

http://ubuntuforums.org/showthread.php?t=1280943

Thanks Yancek...by the time I received your link, I had installed Zorin 6 as the only os thereby forgoing the dual boot option. Zorin 6 is very good and is the option giving support til 2017. Thanks again for all your help.