What can I do about my 70 yr old neighbor?

A lot more info is necessary.
Is your neighbor the one that you are caring for that is indicated in your profile?
If so what are his problems? What are you doing to help him? What needs to be done to help you or help him?

1) attempt to find any local relative of your neighbor and inform them of his/her needs/issues/problems.
2) if you can't locate any family or you do find them but they don't act to help him you must contact APS (Adult Protective Services) to report him as a vulnerable adult (online at your county's Dept of Health and Human Services).

If you think it's a life-threatening situation, call 911.

Without you having any legal permission/authority to help him/her (like assigned Power of Attorney or guardianship) there is nothing much you can do except to get your neighbor on the APS radar and then they will take it from there.

Hi, Shorty440. You appear to be new here. Welcome. Below the subject line you will see a small box in which you can tell us what problem you are facing. Be as specific as you can about the problem, who is causing it, and what you have tried to do so far.
Given that you missed it on this post, instead of making a new post, why not just elaborate in the "answer" area right her.

What seems to be the issue? Are there family members you can call? Office of the Aging if you feel the person is in danger.