Question : 7 disc won't boot

I have built a new pc. I have 7 upgrade ver.
I've installed xp normally.
When I insert the 7 upgrade disc and reboot it bypasses the disc every time as though it's not bootable.  I know it is bootable because I stuck it in on a fresh hdd and it tried to install (but wouldn't of course because it's an upgrade version). What am I missing here?

Bios boot order is correct.
When booting it says press any key to boot from cd but does not respond when I do so.

Thanks in advance.

Answer : 7 disc won't boot

ASCII characters fit in 7 bits, so a data type that holds 8 bits like char would be efficient.
ISO8859 characters fit in 8 bits so a char would also hold them.
for Unicode characters you may want wchar
you say  not going to use to ascii characters, but you do not say what you are going to use, so I'm not sure how to answer more specifically