Is this a new installation and which program - full name and version - are you trying to login into?
Can you post a screenshot of the error message you are getting.
As @CubeAce has commented, the Computer ID is for older versions of Movie Studio/Movie Edit Pro and would not normally be used for program activation is done online.
To use for manual activation when the computer, the program is installed on, is not connected to the Internet, however this is not the same as the computers Windows ID - it is a unique number generated by the software when you select a manual activation/registration via email or online using another computer.
.....Where do I find my ComputerID? The program will not let me log in without the ComputerID....
Personally, I cannot tell you where to find or retrieve the requested ComputerID. My advice, contact Magix Support. Send an email to: infoservice@magix.net and ask them where you can find or retrieve the ComputerID.