Dear Alan:
We feel that we are facing two issues: which one of your choices you should follow, and what is the manner in which you should pursue the chosen path?
Pursuing either one of the choices - certificate in Computer Networking or becoming a Microsoft certified technician - will help you gain knowledge in one of the two areas of high demand in the marketplace. Certificate programs like these can give you a start in a field where you have limited or no knowledge.
So the short answer is yes to your question of whether either of these training program is a worthwhile effort. However, we must hasten to add that the answer also depends on your ambitions. If you have more ambitious plans for your career in the long run, please keep the following in mind. Training programs such as these tend to focus more on how to do things in a particular area, than why you do the things you are trained to do. Lacking a fundamental and deeper knowledge of the "why," these programs tend to have a limited lifespan. Nothing wrong with that, but you must understand that you would have to renew your skills often, through further training/education, so that your skills remain relevant in the marketplace. Depending on your ambitions, somewhere along the way, you may wish to consider pursuing formal college/university education. This education would provide you a deeper knowledge of the field, on which you can continually build more aggressively, with of course greater rewards.
Now let's talk about the more delicate issue of the manner in which you must pursue either of your choices. By your own admission, your performance in your educational endeavors has been somewhat lacking. We strongly encourage you to try your best to perform your best in your next undertaking. Ultimately, it would matter less as to which training program you pursued, than how well you performed on it. Good performance in the training program would demonstrate to your prospective employers what you are capable of accomplishing with the training you have completed.
Alan, we wish you continued success in all your future endeavors.