Diploma

Failing a Diploma doesn't mean you're good for nothing. But ultimately it would leave you only with the same qualifications as that of a 10th pass. Or 12th pass if you cleared 12th and did Diploma. And you would only have a handful of options as a 10th/12th pass person that's not good for your future. The only three ways to deal with the current situation are :
Try to attempt the exam again and clear it. Improve your qualifications further. Everyone has to face failure. How you deal with failure, is what sets you apart from others. Look for a job with your current qualifications. Quit college and do business. Personally I would recommend that you go with option 1. Since I worked in the engineering industry for nearly 5 years, let me tell you marks don't matter in the industry. Only your knowledge does. A person having marks above 90% can't design a product without any knowledge. Clear your papers and look for a job in a small company, where marks don't matter. Then slowly learn your trade and move up the ladder. One day you might be working for an MNC, if everything goes good. Option number 3 is also not bad provided you have sufficient knowledge on the business that you're going to start, but it always comes with a risk. But if any of your family members are into the same business that you plan to start, and are willing to help you with it then your chances of failure will reduce significantly. Option 2 is not something I would recommend, if you want a better quality of life. Above all, don't lose hope.