However, I suspect that @SP. is correct and you actually have a Redemption Code. Licence keys should begin with P3-, redemption codes often with G3 or similar. Please don't quote the code you have in full but tell us the first two characters of it.
I'm 99% certain that is NOT a serial key/licence code but rather a coupon code which you need to redeem, using the link which @SP. provided in his earlier reply.
That code can be used only once so be very careful about entering it on the redemption page. Once it is "accepted" by the Magix servers you should receive an email with the appropriate serial key, which should begin P3-. The email should also include a link to the download of MS11 if you have not already installed it.
If your coupon code is NOT accepted on the redemption page you will need to go back to Guitar Centre and ask for their help with this. Until your code is accepted and registered Magix has no record of your purchase and so cannot help you.
I have used acid pro and studio in the past. Since it was Sonic Foundry. This is beyond bad business. Should have listened to the reviews about how it's just a rip off. I know I'm not the only one that has had this problem. VERY DISAPOINTED!!!!!!!!! Never using any of your products again.
Did you follow the advice previously given to you in this thread? if so, with what results? Unless you are willing to be a little more forthcoming with information there is nothing we, fellow-users, can do to help you!
Also, since these are user to user forums so the products are not ours!
Try checking in your account here under My products to see it the coupon was accepted and a serial number generated for the program using the same email address and password as for here.
If not then as the retailer you purchased from is Guitar Centre you need to take this up with them.
If they are not helpful contact Magix at innfoservice@magix.net and explain the situation to them quoting the Coupon code you recieved.