Hello. I recently purchased a music creator4, but it didn't include the serial number in the box. Where can I get help with this matter? Your help is greatly appreciated.

The only source for serial numbers is Cakewalk support. The problem is Cakewalk stopped selling MC4 in 2009. If the product lacks a serial number it could have been registered by someone else. You might try to get your money back. MC7 is the current version which was released in 2015.

It's 7 years past when Cakewalk discontinued it.... hopefully you didn't pay much... but..... contact Cakewalk first.... if they can't help, and I doubt they can but it's worth a try, get your money back from the seller  since they sold you a non-functional copy of the software, or write it off as a lesson learned about buying from the "aftermarket".  If the seller won't return the money, write a bad review of your experience. That might get some results. Online sellers do not like bad reviews where a customer feels they were ripped off.
 
Then go to the cakewalk store and buy a registered version. It will likely cost you more ....BUT......You get the serial number, a more recent version, and your serial number is kept on line in your account for future use.  And best of all, you know you are 100% legal.

Besides, there are so many really, really nice improvements in the MC line since version 4.   You will really like the new version once you get it.