It sounds like you have an OEM recovery system from the computer manufacturer whereas your friend has a retail Windows XP CD. The two are not interchangable, so your key will not work with his CD or vice versa. You will have to contact the computer manufacturer and request that they send you a set of recovery CDs for a nominal fee. This should be done ASAP for your current installation of Windows XP is technically illegal...you cannot use the same product key one two separate computers at the same time unless you have a special volume licensing agreement. At this point both of you may receive alerts stating that your installations of Windows XP are invalid, be prevented from downloading various Windows updates, etc. Thus, the sooner you address this issue the better.
I recently fixed my PC but had lost the XP HE cd which came with my PC. I have the COA Product Key on the side. Me and a friend used his XPHE CD to install windows. I tried using the CD Key on the side of my PC to activate windows but it did not work. Is it a problem that i used my fiends XP CD to install windows and my CD Key to try to activate.
Any help would be much appreciated.