Also the older the house the harder it is to get rid of the smell.

Paint the floor. Choose the correct product.

Don't paint the floor!!!

Lots more info is needed to begin to try to answer your question....

Where are you located?
What's your climate?
What's the humidity level?
Are you running a dehumidifier? A/C?
Air flow?
Floor drains?
................

A temporary solution is to spray plain apple cider vinegar every alternate day for about 2 weeks. This is help get rid of the odor and eliminate the growth of mildew. Meanwhile as a long term solution investigate for any leaks / cracks etc and have them fixed. Also re painting will give it a fresh look.

most basements need a dehumidifier running.

You can purchase a few bags of charcoal and leave them in the room to absorb the smell ,it works

How about a dehumidifier?

Air it out for a while or try some of the deodorizing things already mentioned. If after 2 weeks the smell remains it means you have moisture issues that must be taken care of before you can put any new product in this space. Basements are tough. They take several different approaches to achieve 1 thing = moisture remediation.

Contact a basement/concrete slab specialist in your area to get some base line moisture testing done. Once testing has been done and base lines measured you can then take a look at the things that need to be done before you can put up plastic, insulation, drywall or flooring. Some remediation methods require access to the cement/slab walls. At this point you are in a great position because the cement is exposed and any remediation needed will already have things ready to roll. Nothing like finding out your moisture remediation requires spraying product onto slab walls that are behind finished walls. That's a real pain!