I have a medical bill that is 3 1/2 years old, but I am able to pay it now, but not sure if I should. It is in collections, of course, and I don't know if it would be worse for my credit to pay it. Can someone tell me the steps I should take, if any? Thank you very much.

In all likelihood, the OC no longer has a relationship with the CA. Maybe they sold the account to the CA in which case paying it will do nothing to improve your score. Even if the OC DOES have a relationship with the CA, just paying it alone (even to the OC) will NOT help your credit no matter what the "experts" tell you. That, I learned the hard way, pre-CB, dang it.

You need to follow WhyChat's dispute process for medical accounts.

Opt out
http://whychat.5u.com/OPTOUTINST.HTML

Delete old addresses from your CRs.

Send the initial dispute letter to the CRAs( list ALL medical accounts, paid or unpaid)
http://whychat.5u.com/hipaadisp.html

Sit back and wait to hear back from the CRAs before making your next move. Post back here in this thread when you get them to find out what your next step should be.