xp installation problems

my friend has been having numerous problems with his pc due to an overloaded, never formatted hdd.

i suggested we reinstall his copy of windows xp using my disc as he has his key stuck to the side of the pc but has no disc, as far as i am aware this should cause no problems.

i have booted from the cd, formatted the relevant drive (C using ntfs and the the necessary files are copied over with no issues.

the pc then reboots as usual and this is where the problem occurs, the first time we rebooted the machine said "problem reading os" on the opening screen and then tried to boot from the cd again.

i have reformatted and reinstalled several times and each the opeing screen says booting from cd and then press any key to boot from cd, it will not continue with the windows setup.

it is probably something stupid and obvious that i am missing but i would be grateful if someone would point it out to me!

thanks