I am from Zimbabwe and applying for Schengen visa (short term) for only 45 days.
How much money is needed in my bank account for me to be given a Schengen visa?
One of the key criteria for short term visit visas (not just for Schengen, but almost anywhere) is that the applicant must be able to support themselves (and their dependents) and should not be a burden on the state. There are many ways to show proof of support; for example, you could have a sponsor that can provide an affidavit of support, your ticket and accommodation can be pre-paid by someone else. However, in the end the application is judged on your individual circumstances.
If you are unable to support yourself for the duration of the trip, do not try to borrow money and place it in your account. This is called funds parking and is almost guaranteed to get your application rejected.
The amount of funds required vary from country to country and also based on what is the purpose and duration of your trip; there is no "fixed amount".
More to the point, if your bank account has large sum of money, and no activity; or it doesn't match the profile of someone in your economic / social status, this is also cause for alarm and possible rejection.